In spite of the learned researches of Professor Williamson, whose name is as closely connected with the pigment as are the names of Schunck and De La Rue with madder and cochineal, Prussian blue is not yet entirely understood. Complex and uncertain in composition, uncertain too in its habitudes, our best course perhaps will be not to attempt a complete survey, but to state briefly those facts which bear on the artist's craft.

Prussian blue is a colour of vast body and wonderful transparency, with a soft velvety richness, and of such intense depth as to appear black in its deepest washes. Notwithstanding it lasts a long time under favourable circumstances, its tints fade by the action of strong light; becoming white, according to Chevreul, in the direct rays of the sun, but regaining its blue colour in the dark; hence that subdued light which is favourable to all colours is particularly so to this blue. Its colour has the singular property of fluctuating, or of coming and going, under certain conditions; and which it owes to the action and reaction by which it acquires or relinquishes oxygen alternately. It also becomes greenish sometimes by a development of the oxide of iron; and is purpled, darkened, or otherwise discoloured by damp or impure air. Time has a neutralizing tendency upon its colour, which forms tints of much beauty with white lead, though they are not equal either in purity, brilliancy, or permanence to those of cobalt and ultramarine. When carefully heated, Prussian blue gives off water and assumes a pale green hue; its colour, therefore, depending on the presence of water, must not be exposed to a high temperature. And as it is likewise injured or destroyed by alkalis, which decompose it into oxide of iron and a soluble prussiate, the blue should be avoided in fresco, on account of the lime; neither should it be employed with pigments of an alkaline nature, nor with hard water containing bicarbonate of lime in solution, but with clean rain or distilled water, either of which is preferable for colours generally.

Prussian blue dries and glazes well in oil, but its great and principal use is in painting deep blues, in which its body helps to secure its permanence, and its transparency gives force to its depth. It is also valuable in compounding deep purples with lake, and is a powerful neutralizer and component of black, to the intensity of which it adds considerably. Prussian blue borders slightly on green, a quality which militates against its use in skies and distances. In spite, however, of its want of, or deficiency in, durability, the old water-colour painters so employed it, neutralized by the addition of a little crimson lake. It is serviceable in mixed tints of greens, affording with light red a sea-green neutral. Dissolved in oxalic acid, the blue is available as an ink, or for tinting maps.

Besides the preceding, there is a Basic Prussian Blue, formed by simply submitting to the air the bluish-white precipitate which falls on adding yellow prussiate of potash to green vitriol. This compound dissolves entirely by continued washing with water, yielding a beautiful deep blue solution, from which the colour may be thrown down in a solid form by the addition of any salt. Probably it was this basic preparation, so cheaply and easily made, that conferred upon Prussian blue the character of staining paper. In name, there is also another variety of this pigment, known as Native Prussian Blue; which is really a native phosphate of iron, occurring as a blue earthy powder, or as a white powder that becomes blue by exposure.

130. ANTWERP BLUE,

Haerlem Blue, Berlin Blue, Mineral Blue, is a lighter and somewhat brighter Prussian blue, with less depth and less permanence. It is a species of lake, having a considerable proportion of aluminous base, to which its paler tint is due. As the stability of Prussian blue rests in a great measure on the marvellous amount of latent colour the pigment contains, when its particles of colour are set farther apart by the intervention of the alumina, the permanence of its hue is endangered. It was remarked, with respect to vitrified pigments, that colour depends on cohesion. More or less, this holds good as regards all pigments; but not only, as was also observed, does colour rest on cohesion, in many instances durability depends likewise. It is only when a colour is stable in itself that its particles will bear separating: native ultramarine, for example, may be weakened almost to white, and will still preserve its hue. If, however, a colour be naturally fugitive, and rely chiefly on its extreme depth for what permanence it possesses, that colour cannot with impunity be paled: witness the cochineal lakes, which the deeper they are, the more durable they are found; and so it is with Prussian blue. Antwerp blue is distinguished from the latter by its more earthy fracture.

131. TURNBULL'S BLUE,

Or Ferricyanide of Iron, is formed by adding the red prussiate of potash to a protosalt of iron. This blue is lighter and more delicate than ordinary Prussian blue, and is believed to resist the action of alkalies longer. It is a question whether the common Prussian blue obtained by oxidizing the precipitate yielded by green vitriol and the yellow prussiate is not in reality this variety. However that may be, there is, as far as permanence goes, little or no difference between the two kinds.

ULTRAMARINES.

ARTIFICIAL ULTRAMARINES

comprise the varieties known as French Ultramarine, French Blue, Brilliant Ultramarine, Factitious Ultramarine, Guimet's Ultramarine, New Blue, Permanent Blue, Gmelin's German Ultramarine, Bleu de Garance, Outremer de Guimet, &c. The unrivalled qualities of native ultramarine prepared from the lapis lazuli rendered it most desirable to obtain an artificial compound which, while possessing similar properties, could be produced in quantity, and at a less costly rate. In demolishing some furnaces employed in making soda, by means of decomposing sulphate of soda, some earth had been found impregnated with a light blue, which was proved to have so close a resemblance to ultramarine as to foster hopes of success. As a stimulus, there was offered a prize of six thousand francs or 500 for the production of artificial ultramarine by the Socit d'Encouragement of Paris, which was won in 1828 by M. Guimet. It is fitting that the discoverer of a colour should excel in its manufacture, and to this day Guimet's ultramarine is the finest made. As an instance of how the researches of different men may, almost simultaneously, lead to the same results, it is curious that very shortly after the problem was also solved by Gmelin.

The cause of the blue colour of ultramarine was long a matter of controversy, but was believed generally to be due to iron. When, however, the discovery of artificial ultramarine was made, this assumption was shown to be false, by the fact that a blue could be obtained with materials perfectly free from iron. The absolutely necessary constituents of ultramarine are silica, alumina, sulphur, and soda; and there is little doubt that the colouring matter consists of hyposulphite of soda and sulphide of sodium: it is certain that the blue colour is dependant on the soda, inasmuch as potash yields an analogous compound which is purely white. A number of substances, such as iron, lime, magnesia, and potash, may be present as impurities, and were, in part at least, purposely added to the earlier manufactures; but they are found to be superfluous. Nevertheless, as regards iron, it is probable that a very small portion, such as is usually contained in the ingredients, greatly facilitates the production of the blue, and may even be essential in some cases.

The colour of ultramarine is brought out by successive heatings. Green portions, more or less in quantity, are often formed in the crucibles, especially on the first ignition. On repeated heating they pass into a blue tint. Artificial ultramarines are said to be seldom entirely freed from all traces of the green modification, and are therefore less beautiful than the natural varieties, having a shade of green or grey. This defect, however, is certainly not discernible in Guimet's products, which sometimes incline so much to purple as to require neutralizing with a little Prussian blue. Depth for depth, the artificial are darker and less azure than the natural varieties, but the superiority of the latter consists not so much in their greater purity of hue, although this is considerable, as in their far greater transparency. The finest French ultramarine is never so transparent as the native; it is brilliant, it is powerful, it is permanent, it is nearly—but only nearly—transparent. Possessing in a subdued degree the characteristics and qualities of the genuine, it works, washes, and dries well; and is useful either in figures, draperies, or landscape. Rivalling in depth, although not equalling in colour, the pure azure of native ultramarine, it answers to the same acid tests, but is sometimes distinguished therefrom by the effervescence which ensues on the addition of an acid. Not a bubble escapes in such case from the natural blue; unless, indeed, as occasionally happens, it retain a portion of alkali, with which it may have been combined in the preparation, but from which it should have been freed. Darkened as a rule by fire, factitious ultramarine becomes dingy blue, and at last white, when strongly ignited for a long time; and is, like the true variety, decolourised by ignition in an atmosphere of hydrogen gas. At a high temperature, this effect is even produced by silica, whence the unfitness of ultramarine for painting on glass or porcelain; and simply by a prolonged red heat the blue is rendered white. Being unaffected by alkalis, it is eligible in mural decoration, and is particularly adapted to siliceous painting, on account of the silica and alumina which it contains, two substances with which a soluble silicate readily unites. If artificial ultramarine be mixed with a soluble silicate, for example silicate of potash, and be laid on a properly prepared ground, it will become so firmly fixed, says Mr. Barff, that no amount of washing nor the slow action of moisture will remove it, or affect its brilliancy. Judging from the behaviour of ultramarine, therefore, if the colours employed in siliceous painting contain silica and alumina, they should adhere as firmly to the surface on which they are placed; and this is really the case. It is possible to produce a mixed solution of aluminate and silicate of potash which will remain liquid for twenty-four hours. If, while in the liquid state, colours are saturated with this solution and allowed to dry, their particles will be very intimately mixed with silica and alumina chemically combined with potash. According to the author quoted, the admixture of silica and alumina does not interfere with the brilliancy or depth of the colours, and the method may be used for all those which are not injured by potash, and are in themselves adapted to the art.

With respect to permanence, the finer varieties of artificial ultramarines may, undoubtedly, be pronounced stable; but, like all other colours, these blues are apt to vary in quality, and inferior kinds are liable to lose their purity in a measure, and become grayer. Moreover, they are made by different processes, and the mode adopted for the manufacture of a pigment not only tells upon the colour, but may influence to some extent its durability. From the following experiment of an ingenious artist and friend of the author, it is evident that the production of artificial ultramarine was not carried in its early days to that state of perfection at which it has now arrived. He took a picture, the sky of which had been recently painted in the ordinary manner with Prussian blue and white; and having painted over the clear part of the sky uniform portions with tints formed of the best factitious ultramarine, cobalt blue, and genuine ultramarine, so as to match the ground of the sky, and to disappear to the eye thereon by blending with the ground, when viewed at a moderate distance, he set the picture aside for some months. Upon examination, it appeared that the colour of these various blue pigments had taken different ways, and departed from the hue of the ground: the factitious ultramarine had blackened, the cobalt blue greened, the genuine ultramarine remained a pure azure, like a spot of light, while their ground, the Prussian blue sky, seemed by contrast with the ultramarine of a grey or slate colour.

Other things being equal, those artificial ultramarines are most durable which possess the most colour; and all are, perhaps, most permanent in water. If used in that vehicle, care should be taken to employ a gum free from acid; also, whether in water or oil, not to compound the blue with a pigment which may possibly contain acid, such as constant white. Acid, as we have said, is the great test for ultramarine; whence if a sample be sophisticated with cobalt, its blue colour will not be entirely destroyed. With high-class artistic pigments, however, adulteration is the exception and not the rule. It is as a powder-blue for the washtub that ultramarine gets disguised, when it is ground up with soda-ash, chalk, gypsum, &c., and sold sometimes under its own name, but more frequently as superfine Saxon smalts.

132. BRILLIANT ULTRAMARINE,

lately called Factitious Ultramarine, is a specially fine preparation of M. Guimet, presenting the nearest approach to the natural product of any artificial ultramarine, both in transparency, purity of hue, and chemical characteristics. Equalling in depth and power the ordinary French ultramarine, it possesses greater clearness, beauty, and brightness; and has, in a subdued degree, that quality of light in it, and of the tint of air, which forms so distinguishing a feature in the native blue.

133. FRENCH ULTRAMARINE,

or French Blue, is a rich deep colour, but less transparent and vivid than the preceding variety, which is preferable in unmixed tints. For compound hues, French blue is sufficiently well adapted, and is extremely useful. With aureolin and burnt Sienna, or Vandyke brown, it affords valuable autumn greens; and with lamp black, or lamp black and light red, good stormy clouds. A sombre gray for distant mountains is furnished by French blue and madder brown, with a very little gamboge; and a deep purple for sunsets, by the blue and purple madder, or Indian red and rose madder. With cadmium and orient yellows, sepia, viridian, and many other colours, this ultramarine is of service.

134. NEW BLUE

Is confined to water-colour painting, and is an artificial ultramarine, holding a middle position between French blue and permanent blue, being less deep than the one and less pale than the other. It may be said to hover in tint between a rich ultramarine and cobalt.

135. PERMANENT BLUE

Is a pale ultramarine, with a cobalt hue; and, in spite of its name, less permanence than belongs to the richer and deeper sorts. What Antwerp blue is to Prussian blue, this is to French blue—that is, as regards colour. With respect to durability, however, permanent and Antwerp blues cannot be compared; the former being a weakened variety of a stable, and the latter a weakened variety of a semi-fugitive, pigment. Hence permanent blue justifies its name, although that name would be more suited to the brilliant, or French, ultramarine.

136. GENUINE ULTRAMARINE,

_Native Ultramarine_, _Natural Ultramarine_, _Real Ultramarine_, _True Ultramarine_, _Ultramarine_, _Pure _Ultramarine_, _Azure_, _Outremer_, _Lazuline_, _Lazulite Blue_, and _Lazurstein_. This most costly, most permanent, and most celebrated of all pigments, is obtained by isolating the blue colouring matter of the _lapis lazuli_, a stone chiefly brought from China, Thibet, and the shores of Lake Baikal. About the antiquity of the stone, and its colour, much has been written, and many conflicting statements have been made; but there is little doubt that our lapis lazuli was the sapphire of the ancients; and that the first certain mention of ultramarine occurs in a passage of Arethas, who lived in the eleventh century, and who, in his exposition of a verse in the book of Revelation, says, the sapphire is that stone of which _lazurium_, as we are told, is made. It has been common to confound ultramarine with the _cyanus_ and _coeruleum_ of the ancients; but their cyanus, or Armenian blue, was a kind of mineral or mountain blue, tinged with copper; and their coeruleum, although it may sometimes have been real ultramarine, was properly and in general a copper ochre. That ultramarine was known to the ancients there seems every probability, for it is certain they were acquainted with the stone; and modern travellers describe the brilliant blue painting still remaining in the ruins of temples of Upper Egypt as having all the appearance of ultramarine. Whether it is so or not, however, could only be proved by analysis; for, be it recollected, although the colour had preserved its hue during so many centuries, it had been completely buried, and therefore most perfectly secluded from light and air. Mr. Layard, in his 'Nineveh,' referring to some painted plaster, remarks that "The colours, particularly the blues and reds, were as brilliant and vivid when the earth was removed from them as they could originally have been; but, on exposure to the air, they faded rapidly." In all likelihood, these were of organic, or semi-organic, origin, prepared in some such manner as that mentioned by Pliny, who speaks of an earth which, when boiled with plants, acquired their blue colour, and was in some measure inflammable. As a pigment, cobalt was unknown to the ancients; but to these vegetable and copper blues of theirs, a third blue may perhaps be added. Experiments made upon blue tiles, found in a Roman tesselated foot-pavement at Montbeillard, showed that the colour was due to iron. M. Gmelin has proved that a blue tint can be imparted to glass and enamel by means of iron; and it is probable that the ancients were first induced by the blue slag of their smelting-houses to study the colouring of glass with iron; that in this art they acquired a dexterity not possessed at present, and that they employed their iron-smalt as a pigment, as we do our smalt of cobalt. To sum up, there are grounds for believing that the ancients were acquainted with copper blues, vegetable blues, and iron blues; and that, consequently, the blue described by travellers as having all the appearance of ultramarine may, or may not, be that pigment.

Lapis lazuli, or lazulite, is usually disseminated in a rock, which contains, among other substances, a fine white lazulite. In the Muse Minralogique of Paris are two splendid specimens of the stone, in which is seen the transition from the azure to the white. According to the quantity and quality of blue present, the lapis varies from an almost uniform tint of the deepest indigo-blue to grayish-white, dotted and streaked at intervals with pale blue. The exceeding beauty of good samples has caused the lazulite to be much sought after, both as a gem for adorning the person, and for inlaid works in ornamental decoration. In China the stone is highly esteemed, being worn by mandarins as badges of nobility conferred only by the Emperor; and in the apartments of a summer palace near St. Petersburg, the walls are covered with amber, interspersed with plates of this costly lapis. Besides the colouring principle of the lazulite, there are always more or less mica and iron pyrites, the latter a lustrous yellow bisulphide of iron, which has often been mistaken for pellets of gold. Having chosen portions of the stone most free from these impurities, it is simply requisite to reduce them to an impalpable powder to obtain a blue pigment; and probably this was the original mode of preparing it before the discovery of the modern process. This curious method, which is mechanical rather than chemical, depends for its success on the character and proportions of the materials employed, as well as on the nicety of working. When well carried out, it perfectly isolates the blue from all extraneous matter, yielding the colour at first deep and rich, then lighter and paler, and lastly of that gray tint which is known by the name of Ultramarine Ash. The refuse, containing little or no blue, furnishes the useful pigment, Mineral Gray.

The immense price of ultramarine—or, as it was at first called, azurrum ultramarinum, blue beyond-the-sea—was almost a prohibition to its use in former times. It is related that Charles I. presented to Mrs. Walpole, and possibly to Vandyke also, five hundred pounds worth of ultramarine, which lay in so small a compass as only to cover his hand. Even in these days, despite the introduction of artificial ultramarines, the native product continues costly, commanding in proportion to its intensity and brightness, from two to eight guineas an ounce. To say, however, that the merits of the blue at least equal its expense, is to give the genuine ultramarine no more than its due. It has, indeed, not earned its reputation upon slight pretensions, being, when of fine quality, and skilfully prepared, of the most exquisitely beautiful blue, ranging from the utmost depth of shadow to the highest brilliancy of light and colour,—transparent in all its shades, and pure in all its tints. A true medial blue, when perfect, partaking neither of purple on the one hand, nor of green on the other, it sustains no injury either by damp and impure air, or by the intensest action of light, and is so eminently durable, that it remains unchanged in the oldest paintings. Drying well, working well in oil and fresco, ultramarine may be safely compounded with pigments generally, excepting only an acid sulphate of baryta or constant white. The blue has so much of the property of light in it, and of the tint of air—is so purely a sky-colour, and hence so singularly adapted to the direct and reflex light of the sky, and to become the antagonist of sunshine—that it is indispensable to the painter. Moreover, it is so pure, so true, so unchangeable in its tints and glazings, as to be no less essential in imitating the marvellous colouring of nature in flesh and flowers. To this may be added that it enters so admirably into purples, blacks, greens, grays, and broken hues, that it has justly obtained the character of clearing or carrying light and air into all colours, both in mixture and glazing, as well as gained a sort of claim to universality throughout a picture.

Nevertheless, ultramarine is not always entitled to the whole of this commendation. Frequently it is coarse in texture, in which case it is apparently more deep and valuable; yet such blue cannot be used with effect, nor ground fine without injuring its colour. Again, it is apt to be separated in an impure state from the lapis lazuli, which is an exceedingly varying and compound mineral, abounding with earthy and metallic parts in different states of oxidation and composition: hence ultramarine sometimes contains iron as a red oxide, when it has a purple cast; and sometimes the same metal as a yellow oxide, when it is of a green tone; while often it retains a portion of black sulphuret of iron, which imparts a dark and dusky hue. Occasionally, it is true, artists have preferred ultramarine for each of these tones; still are they imperfections which may account for various effects and defects of this pigment in painting. Growing deeper by age has been attributed to ultramarine; but it is only such specimens as would acquire depth in the fire that could be subject to the change; and it has been reasonably supposed that in pictures wherein other colours have faded, it may have taken this appearance by contrast. Ultramarine, prepared from calcined lapis, is not liable to so deepen; but this advantage may be purchased at some sacrifice of the vivid, warm, and pure azure colour of the blue produced from unburnt stone. We have frequently found ultramarine to be darkened, dimmed, and somewhat purpled by ignition; and the same results ensue, in many instances, when the lazulite is calcined. In burning the stone, the sulphur of the pyrites is in a great measure expelled, and during its expulsion has probably a deteriorating influence on the beauty of the colour: our belief in this being so is strengthened by the fact that certain samples of ultramarine, ignited with sulphur, were not improved thereby. Similar effects are likewise caused by a careless or improper mode of treatment, for the finest lapis may yield dingy blues, containing particles of mica, metal, &c., and possessing a dull green, black, or purple hue. Of course the perfection of the pigment is dependant to a large extent upon the quality of the stone itself.

Though unexceptionable as an oil-colour, both in solid painting and glazing, it does not work so well as some other blues in water; nor is it, unless carefully prepared, so well adapted for mixed tints, on account of a gritty quality, of which no grinding will entirely divest it, and which causes it to separate from other pigments. When extremely fine in texture, however, or when a considerable portion of gum, which renders it transparent, can be employed to give connexion or adhesion while flowing, it becomes no less valuable in water than in oil; but when its vivid azure is to be preserved, as in illuminated manuscripts and missals, little gum must be used. The fine greens, purples, and grays of the old masters, are often unquestionably compounds of ultramarine; and formerly it was the only blue known in fresco. Pure ultramarine varies in shade from light to dark, and in hue from pale warm azure to the deepest cold blue.

Native ultramarine consists of silica, alumina, sulphur, and soda; its colouring matter seeming to be due to hyposulphite of soda and sulphide of sodium. In these respects, as well as in that of being decolourised by acids, the natural product resembles the artificial. As a precious material, the former has been subject to adulteration; and it has been dyed, damped, and oiled to enrich its appearance; attempts of fraud, however, which may be easily detected. In the preceding edition of this work the author adds—"and the genuine may be as easily distinguished from the spurious by dropping a few particles of the pigment into lemon-juice, or any other acid, which almost instantly destroys the colour of the true ultramarine totally, and without effervescence." With this statement, so far as it pretends to be a test for the two kinds, we are not inclined to agree. Genuine ultramarine is always decolourised by acids; but it depends on the mode and nicety of its preparation whether it is decolourised without effervescence: that this is the case the author himself admits in his article on artificial ultramarine. Moreover, the "violent effervescence" which he describes as ensuing on the latter being dropped into an acid, does not of necessity take place: in M. Guimet's finest variety, the brilliant ultramarine, acid produces little or no effervescence. Seeing, therefore, that both sorts are decolourised by acids, and that both may or may not effervesce therewith, the acid test must be considered fallacious. Experiments made with different samples of each, showed that native ultramarines offered greater resistance to acid than the artificial, taking longer to decolourise; and that the residues of the first were in general of a purer white than those of the last. It was also found that the brilliant ultramarine, above referred to, was less readily decolourised than other French or German kinds.

* * * * *

137. Blue Carmine.

In a former edition of this work there appeared the following:—"Blue carmine is a blue oxide of molybdenum, of which little is known as a substance or as a pigment. It is said to be of a beautiful blue colour, and durable in a strong light, but is subject to be changed in hue by other substances, and blackened by foul air: we may conjecture, therefore, that it is not of much value in painting." In his estimate of this colour the author was certainly right. It is formed when a solution of bichloride of molybdenum is poured into a saturated, or nearly saturated, solution of molybdate of ammonia. A blue precipitate falls, which is a molybdate of molybdic oxide, hydrated, and abundantly soluble in water. When dried, it furnishes a dark blue powder, resembling powdered indigo, having a bitter, rough, metallic taste, and reddening litmus strongly. The solubility of this hydrated oxide is alone fatal to its employment as a pigment. It may, indeed, be rendered comparatively insoluble in water by ignition; but the anhydrous oxide so obtained is nearly black, and as a colour worthless.

A more eligible preparation is the molybdate of baryta, produced by mixing solutions of molybdate of potash and acetate of baryta. A white, flocculent precipitate results, which rapidly condenses to a crystalline powder, and turns blue on ignition. It is, however, a costly compound, of little merit, and not likely to come into use. It is insoluble in water.

138. Blue Ochre,

which has been improperly called Native Prussian Blue, is a native hydrated phosphate of iron of rare occurrence, found with iron pyrites in Cornwall, and also in North America. What Indian red is to the colour red, and Oxford ochre to yellow, this pigment is to the colour blue, being sober and subdued rather than brilliant. It has the body of other ochres, more transparency, and is of considerable depth. Both in water and oil it works well, dries readily, and does not suffer in tint with white lead, nor change when exposed to the action of strong light, damp, or impure air. As far as its powers extend, therefore, it is an eligible pigment, though not generally employed nor easily procured; it may, however, be artificially prepared. Answering to similar acid tests as ultramarine, it is distinguished therefrom by assuming an olive-brown hue on exposure to a red heat.

139. Cobalt Prussian Blue.

Gmelin states that yellow prussiate of potash yields with a solution of oxalate of sesquioxide of cobalt a blue resembling Prussian blue—that, in fact, there can be obtained a Prussian blue with a base of cobalt instead of iron. In the moist state, the similarity is sufficiently great, but when washed and dried, the product is, with us, a dingy slate colour. Possibly, if such a blue could be produced, it might exceed in permanence the ferro- and ferri-cyanides of iron. Of course the compound would be much more expensive.

Copper Blues

are now seldom or never employed as artists' pigments. The following are the principal varieties:—

140. Bice,

Blue Bice, Iris, Terre Bleu, was prepared, when true, from the Armenian stone, which is a calcareous kind of stone coloured with copper. It was of a light bright hue, but is completely superseded by pale ultramarine. The Persian lazur appears to have been a similar pigment, being a sort of copper ore, which, when the stone was pounded and sifted, furnished a fine paint, very bright and pleasant. It could not, however, stand the effects of the atmosphere like the Tartarian lazur or lapis lazuli, in the course of time becoming of a dark and dismal colour.

Ground smalts, blue verditer, and other pigments, have passed under the name of bice.

141. Blue Ashes, or Mountain Blue,

are both hydrated carbonates of copper, the first being artificially prepared, and the second found native in Cumberland. Neither is durable, especially in oil; and, as pigments, both are precisely of the character of verditer. By treating the natural malachite green with an alkali, it may be converted into blue.

142. Blue Verditer,

or Verditer, is an oxide of copper, formed by precipitating nitrate of copper with lime. It is of a beautiful light blue colour, little affected by light, but greened and ultimately blackened by time, damp, and impure air—changes which ensue even more rapidly in oil than in water. It is mostly confined to distemper painting and paper-staining.

143. Egyptian Blue,

called by Vitruvius, Coeruleum, is frequently found on the walls of the temples in Egypt, as well as on the cases enclosing mummies. Count Chaptal, who analysed some of it discovered in 1809 in a shop at Pompeii, found that it was blue ashes, not prepared in the moist manner, but by calcination. He considers it a kind of frit, of a semi-vitreous nature; and this would appear to be the case from Sir H. Davy obtaining a similar colour by exposing to a strong heat, for two hours, a mixture of fifteen parts of carbonate of soda, twenty of powdered flints, and three of copper. The colour is very brilliant when first made, and retains its hue well in distemper and decorative painting; but it has the common defect of copper blues of turning green in oil, when ground impalpably for artistic use. One remarkable effect of this copper smalt—for it is nothing else—is, that by lamp-light it shows somewhat greenish, but shines by day with all the brightness of azure. Mrime believes that Paul Veronese employed this sort of blue in many of his pictures where the skies have become green.

144. Saunders Blue,

a corrupt name from Cendres Bleues, the original denomination probably of ultramarine ashes, is of two kinds, the natural and artificial. The first is a blue mineral found near copper mines, while the last is simply a verditer.

145. Schweinfurt Blue,

or Reboulleau's Blue, is prepared by fusing together equal weights of ordinary arseniate of protoxide of copper and arseniate of potash, and adding one-fifth its weight of nitre to the fused mass. The result is, so to speak, a sort of blue Scheele's green, into which latter colour it soon passes when rubbed with oil.

146. Cotton Seed Blue.

Cotton seed oil is bleached by treatment with either carbonate of soda or caustic lime. In both cases, a considerable residue is left after drawing off the bleached oil. This residue is treated with sulphuric acid, and distilled at a high temperature, when there is left a compact mass of a deep greenish-blue colour. On further treatment of this mass with strong sulphuric acid, the green tint disappears, and a very intense pure blue colour is produced. The blue mass is a mixture of the coloured substance with some sulphuric acid, sulphate of soda, and fats. The two former may be removed by washing with water; the latter by treatment with naptha. Alcohol now dissolves the blue colour, and water precipitates it from the solution chemically pure.

This blue has not been introduced as a pigment; and of its permanence, and other attributes, we know nothing.

147. Gold Blue.

Gold purple, under the name of Purple of Cassius, was once very well known: a like compound of tin and gold may be made to yield a blue. Resembling indigo, the colour is not remarkably brilliant, and, unless several precautions are carefully observed, is rather violet than blue. When obtained, the colour must be quickly washed by decantation, or it changes first to violet and then to purple. Its costliness, lack of brightness, and tendency to redden, are against its employment on the palette. In enamelling it would doubtless preserve its colour, and in exceptional cases might be useful.

148. Iodine Blue.

It is curious that iodine, which gives a yellow with lead, should also afford a blue with the same metal. When a solution of iodine in aqueous soda (carbonate of soda is not so good) is added to nitrate or acetate of lead-oxide, a transient violet-red precipitate falls, which decomposes spontaneously under water, yielding iodine and a beautiful blue powder. The colour, however, is exceedingly fugitive, even the carbonic acid of the air separating iodine from it and forming a lead salt. Bearing in mind the scarlet iodide of mercury, iodine is capable of furnishing the three primary colours, distinguished alike by their brilliancy and fugacity.

149. Iridium Blue.

The rare metal iridium affords a blue which is a mixture of the oxide and the sesquioxide. But being slightly soluble in water and decolourised by sulphuretted hydrogen, it would not, other considerations apart, be an acquisition.

150. Manganese Blue.

An aqueous solution of permanganate of potash yields with baryta-water a violet mixture, which afterwards becomes colourless, and deposits a blue precipitate. This retains its colour after washing and drying, but cannot be recommended as a pigment, being liable to suffer in contact with organic substances, which deoxidize and decolourize the manganates and permanganates.

151. Platinum Blue.

With mercurous nitrate, the platinocyanide of potassium forms a thick smalt blue, and the platinidcyanide a dark blue precipitate. The compound is a mixture of platino- or platinidcyanide of mercury and mercurous nitrate. Upon the presence of the latter the colour seems to depend, for on washing with cold water containing nitric acid, the nitrate is not removed nor the blue affected; but boiling water extracts the nitrate and leaves a white residue. A blue containing mercurous nitrate must necessarily be injured by impure air, and be otherwise objectionable.

152. Tungsten Blue

is an oxide formed by the action of various deoxidizing agents on tungstic acid. It remains unaltered in the air at ordinary temperatures, is opaque, and of a blackish indigo-blue colour. As a pigment, there is little to recommend it.

153. Wood-Tar Blue.

The colours obtained from coal-tar have become household words, and it is not impossible that those from wood-tar may be some day equally familiar. At present wood-tar is comparatively unexplored, but the fact that picamar furnishes a blue is at least as suggestive and hopeful as that transient purple colouration by which aniline was once chiefly distinguished. As aniline is a product of coal-tar, so picamar is a product of wood-tar; and as the former gives a purple with hypochlorites, so the latter yields a blue with baryta-water. Both are distinguished by coloured tests, but there is this advantage in the picamar blue—it is comparatively permanent.

Picamar blue is produced when a few drops of baryta-water are added to an alcoholic solution of impure picamar, or even to wood-tar oil deprived of its acid. The liquor instantly assumes a bright blue tint, which in a few minutes passes into an indigo colour. From [Greek: pitta] pitch, and [Greek: kallos] ornament, the blue is named Pittacal.

The mode of separating pittacal has not been clearly described. Dumas states, that when precipitated in a flocculent state from its solutions, or obtained by evaporation, it closely resembles indigo, and, like it, acquires a coppery hue when rubbed. It is inodorous, tasteless, and not volatile; and is abundantly soluble in acetic acid, forming a red liquid, which, when saturated by an alkali, becomes of a bright blue. It is represented as a more delicate test of acid and alkalis than litmus. With acetate of lead, protochloride of tin, ammonio-sulphate of copper, and acetate of alumina, it yields a fine blue colour with a tint of violet, said not to be affected by air or light, and therefore recommended for dyeing.

Like indigo, pittacal is believed to contain nitrogen, but its ultimate composition has not been accurately determined. Dumas considers it identical with a blue product obtained in 1827 from coal-tar by MM. Barthe and Laurent. If this be the case, its greater stability over coal-tar blues and colours generally admits of doubt. That, however, has yet to be ascertained. Our object in noticing this blue has been two-fold: first, to direct attention to wood-tar as a possible source of colour; and secondly, to point to pittacal as a possible substitute for indigo, possessing greater durability.

154. Zinc-Cobalt Blue.

Cobalt, as furnishing a blue colour, is usually associated with alumina, silica, or tin; and, as furnishing a green colour, with zinc. But there is obtainable a compound of zinc and cobalt which gives a blue not only free from green, but inclining rather to red. It is made by adding to a solution of ordinary phosphate of soda in excess a solution first of sulphate of zinc and then of sulphate of cobalt, and washing and igniting the precipitate. The result is a vitreous blue with a purple cast, of little body, and exceedingly difficult to grind. Altogether, it is not unlike smalt, over which it has no advantages as an artistic pigment either in colour or permanence. For tinting porcelain, however, it is admirably adapted, imparting thereto a very pure dark blue of extraordinary beauty. This blue is distinguished from smalt by dissolving in acetic acid.

* * * * *

Compared with the wide range of yellows, or even with reds, the artist finds the number of his blues limited. The perfect native and excellent artificial ultramarines, the good blues of cobalt, the fair Prussian blue, and the doubtful indigo, are the four varieties he has for years been in the habit of using, and is still mainly dependent on. Our division, therefore, into permanent, semi-stable, and fugitive, is easily effected.

In the front rank, pre-eminent among blues as among pigments generally, stands genuine ultramarine. Behind it, are the artificial ultramarines; and behind them again, cobalt and cerulian blue. To a greater or less extent, all these are durable.

Among the semi-stable, must be classed cyanine or Leitch's blue, smalt, and Prussian blue.

To the fugitive, belong indigo and the somewhat more permanent intense blue, Antwerp blue, and the copper blues.

In this list of blues, which grace or disgrace the palette of the present day, there is one colour which, although not permanent, is almost indispensable. As yet, the chemist cannot in all cases lay down the law as to what pigments may or may not be employed. The painter who unnecessarily uses fugitive colours must have little love for his craft, and a poor opinion of the value of his work; but, even with the best intentions and the utmost self-esteem, the artist cannot always confine himself to strictly stable pigments. He has no right to use orpiment instead of cadmium yellow, or red lead instead of vermilion, or copper blue instead of cobalt: he has no business to employ indigo when Prussian blue saddened by black will answer his purpose; but—what pigment can he substitute for Prussian blue itself? None. In its wondrous depth, richness, and transparency, it stands alone: there is no yellow to compare with it, no red to equal it, no blue to rival it. In force and power it is a colour among colours, and transparent beyond them all. The great importance of transparent pigments is to unite with solid or opaque colours of their own hues, giving tone and atmosphere generally, together with beauty and life; to convert primary into secondary, and secondary into tertiary colours, with brilliancy; to deepen and enrich dark colours and shadows, and to impart force and tone to black itself. For such effects, no pigment can vie with Prussian blue. What purples it produces, what greens it gives, what a matchless range of grays; what velvety glow it confers, how it softens the harshness of colours, and how it subdues their glare. No; until the advent of a perfect palette, the artist can scarcely part with his Prussian blue; nor can the chemist, who has nothing better to offer, hold him to blame. It is for Art to copy Nature with the best materials she possesses: it is for Science to learn the secrets of Nature, and turn them to the benefit of Art.



CHAPTER XI.

ON THE SECONDARY, ORANGE.

Orange is the first of the secondary colours in relation to light, being in all the variety of its hues composed of yellow and red. A true or perfect orange is such a compound of red and yellow as will neutralize a perfect blue in equal quantity either of surface or intensity; and the proportions of such compound are five of perfect red to three of perfect yellow. When orange inclines to red, it takes the names of scarlet, poppy, &c.: in gold colour, &c., it leans towards yellow. Combined with green it forms the tertiary citrine, and with purple the tertiary russet: it also furnishes a series of warm semi-neutral colours with black, and harmonizes in contact and variety of tints with white.

Orange is an advancing colour in painting:—in nature it is effective at a great distance, acting powerfully on the eye, diminishing its sensibility in accordance with the strength of the light in which it is viewed. It is of the hue, and partakes of the vividness of sunshine, as it likewise does of all the powers of its components, red and yellow. Pre-eminently a warm colour, being the equal contrast of or antagonist to blue, to which the attribute of coolness peculiarly belongs, it is discordant when standing alone with yellow or with red, unresolved by their proper contrasts or harmonizing colours, purple and green. As an archeus or ruling colour, orange is one of the most agreeable keys in toning a picture, from the richness and warmth of its effects. If it predominate therein, for the colouring to be true, the violet and purple should be more or less red, the red more or less scarlet, the yellow more or less intense and orange, and the orange itself be intense and vivid. Further, the greens must lose some of their blue and consequently become yellower, the light blues be more or less light grey, and the deep indigo more or less marrone.

Although the secondary colours are capable of being obtained by admixture of the primaries in an infinitude of hues, tints, and shades; yet simple original pigments of whatever class—whether secondary, tertiary, or semi-neutral—are, it has been said before, often superior to those compounded, both in a chemical and artistic sense. Hence a thoroughly good original orange is only of less value and importance than a thoroughly good original yellow, a green than a blue, or a purple than a red. To produce pure and permanent compound hues requires practice and knowledge, and we too often see in the works of painters combinations neither pleasing nor stable. Colours are associated with each other which do not mix kindly, and compounds formed of which one or both constituents are fugitive. As a consequence, mixed tints are frequently wanting in clearness, and, where they do not disappear altogether, resolve themselves into some primary colour; orange becoming red by a fading of the yellow, green yellow by a fading of the blue, and purple blue by a fading of the red. Again, with regard to compound tints, there is the danger of one colour reacting upon and injuring another, as in the case of greens obtained from chrome yellow and Prussian blue, where the former ultimately destroys the latter. Of course a mixture of two permanent pigments which do not react on each other will remain permanent; the green, for instance, furnished by aureolin and native ultramarine lasting as long as the ground itself. To produce, however, the effects desired, the artist does not always stop to consider the fitness and stability of his colours in compounding, even if he possess the needed acquaintance with their physical and chemical properties. At all times, therefore, but especially when such knowledge is slight, good orange, &c., pigments are of more or less value, as by their use the employment of inferior mixtures is to a great extent avoided. In mingling primary with primary, if one colour does not compound well with the other, or is fugacious, the result is failure; but a secondary is not so easily affected by admixture: a green, for example, is seldom quite ruined by the injudicious addition of blue or yellow; and even if either of the latter be fugitive, the green will remain a green if originally durable. Thus the secondaries, if they are not already of the colour required, may be brightened or subdued, deepened or paled, with comparative impunity. The artist who, from long years of experience, knows exactly the properties and capabilities of the colours he employs, may in a measure dispense with secondary pigments, and obtain from the primaries mixed tints at once stable, beautiful, and pure; but even he must sometimes resort to them, as when a green like emerald or viridian is required, which no mixture of blue and yellow will afford. The primaries, by reason of their not being able to be composed of other colours, occupy the first place on the palette, and are of the first importance; but the secondaries are far too useful to be disregarded, and have a value of their own, which both veteran and tyro have cause to acknowledge.

The list of original orange pigments was once so deficient, that in some old treatises on the subject of colours, they are not even mentioned. This may have arisen, not merely from their paucity, but from the unsettled signification of the term orange, as well as from improperly calling these pigments reds, yellows, &c. In these days, however, orange pigments are sufficiently numerous to merit a chapter to themselves; they indeed comprise some of the best colours on the palette.

155. BURNT SIENNA,

or Burnt Terra di Sienna, is calcined raw Sienna, of a rich transparent brown-orange or orange-russet colour, richer, deeper, and more transparent than the raw earth. It also works and dries better, has in other respects the qualities of its parent colour, and is a most permanent and serviceable pigment in painting generally. For the warm tints in rocks, mud banks, and buildings, this colour is excellent. When mixed with blue it makes a good green; furnishing a bright green with cobalt, and one much more intense with Prussian blue. For the foresea, whether calm or broken by waves, it may be employed with a little madder; while compounded with a small portion of the latter and lamp black, it meets the hues of old posts, boats, and a variety of near objects, as the tints may be varied by modifying the proportions of the component colours. Used with white, it yields a range of sunny tones; and with aureolin or French blue and aureolin will be found of service, the last compound giving a fine olive green. Similar but fugitive greens are afforded by admixture of burnt Sienna with indigo and yellow or Roman ochre, or raw Sienna; tints which may be saddened into olive neutrals by the addition of sepia, and rendered more durable by substituting for indigo Prussian blue and black. Mixed with viridian, it furnishes autumnal hues of the utmost richness, beauty, and permanence; and, alone, is valuable as a glaze over foliage and herbage. For the dark markings and divisions of stones a compound of Payne's gray and burnt Sienna will prove serviceable; while for red sails the Sienna, either by itself, with brown madder, or with Indian red, cannot be surpassed. For foregrounds, banks and roads, cattle and animals in general, burnt Sienna is equally eligible, both alone and compounded. It has a slight tendency to darken by time.

156. CADMIUM ORANGE

was first introduced to the art-world at the International Exhibition of 1862, where it was universally admired for its extreme brilliancy and beauty, a brilliancy equalled by few of the colours with which it was associated, and a beauty devoid of coarseness. We remember well the power it possessed of attracting the eye from a distance; and how, on near approach, it threw nearly all other pigments into the shade. It has in truth a lustrous luminosity not often to be met with, added to a total absence of rankness or harshness. A simple original colour, containing no base but cadmium, it is of perfect permanence, being uninjured by exposure to light, air or damp, by sulphuretted hydrogen, or by admixture. Having in common with cadmium sulphides a certain amount of transparency, it is invaluable for gorgeous sunsets and the like, either alone or compounded with aureolin. Of great depth and power in its full touches, the pale washes are marked by that clearness and delicacy which are so essential in painting skies. As day declines, and blue melts into green, green into orange, and orange into purple, the proper use of this pigment will produce effects both glowing and transparent. Transparency signifies the quality of being seen through or into; and in no better way can it be arrived at than by giving a number of thin washes of determined character, each lighter than the preceding one. With due care in preserving their forms, from the commencement to the termination, such washes of orange will furnish hues the softest and most aerial. For bits of bright drapery, a glaze over autumn leaves, and mural decoration, this colour is adapted; while in illumination it supplies a want formerly much felt. "With the exception of scarlet or bright orange," said Mr. Bradley, nine or ten years since, in his Manual of Illumination, "our colours are everything we could wish." As an original pigment, a permanent scarlet does not yet exist; but the brilliancy of cadmium orange cannot be disputed, nor its claim to be the only unexceptionable bright orange known. It even assists the formation of the other colour: remarks the author mentioned, "Brilliancy is obtained by gradation. Suppose a scarlet over-curling leaf, for example. The whole should be painted in pure orange, with the gentlest possible after-touch of vermilion towards the corner under the curl. When dry, a firm line—not wash—of carmine, (of madder, preferable.—Ed.), passed within the outline on the shade side only of the leaf, will give to the whole the look of a bright scarlet surface, but with an indescribable superadded charm, that no merely flat colour can possess." In the same branch of art, illumination, cadmium orange, opposed to viridian, presents a most dazzling contrast, especially if relieved by purple.

157. CHINESE ORANGE

belongs to the coal-tar colours, and ought strictly to have been classed therewith. We have preferred, however, to keep it separate, because, as Chinese Orange, it was introduced as a pigment, and has not been employed as a dye. In colour, it somewhat resembles burnt Sienna, enriched, reddened, brightened, and made more transparent, by admixture with crimson lake. From its behaviour, it would seem to be composed of yellow and red, such a compound as magenta and aniline yellow would afford. Its pale washes are uncertain, being apt to resolve themselves into red and yellow, of which the latter appears the most permanent; for, on exposure to light and air, the red more or less flies, leaving here a yellow, and there a reddish-yellow ground: in places both red and yellow disappear. Like all fugitive colours, it is comparatively stable when used in body; but even then it entirely loses its depth and richness, and in a great measure its redness, becoming faded and yellowish. In thin washes or glazing it is totally inadmissible; and, being neither a red, an orange, nor a brown, is unsuited to pure effects. Nevertheless, where it need not be unduly exposed; in portfolio illuminations, for instance, the richness, subdued brilliancy, and transparency of this pigment, justify its adoption. It is not affected by an impure atmosphere.

Aniline colours may be adapted for oil painting by dissolving them in the strongest alcohol, saturating the solution with Dammar resin, filtering the tincture, and pouring the filtrate either on pure water or solution of common salt, stirring well all the time. The water or brine solution must be at least twenty times the bulk of the tincture. The colour after being collected on a filter, washed, and dried, can be ground with linseed oil, poppy oil, or oil varnishes.

158. CHROME ORANGE,

Orange Chrome, or Orange Chromate of Lead, is a sub-chromate of lead of an orange-yellow colour, produced by the action of an alkali on chrome yellow. Like all the chromates of lead, it is characterized by power and brilliancy; but also by a rankness of tone, a want of permanence, and a tendency to injure organic pigments. By reason of its lead base it is subject to alteration by impure air, but is on the whole preferable to the chrome yellows, being liable in a somewhat less degree to their changes and affinities. As, however, a colour has no business to be used if a better can be procured, the recent introduction of cadmium orange renders all risk unnecessary.

159. MARS ORANGE,

Orange de Mars, is a subdued orange of the burnt Sienna class, but without the brown tinge that distinguishes the latter. Marked by a special clearness and purity of tone, with much transparency, it affords bright sunny tints in its pale washes, and combines effectively with white. Being an artificial iron ochre it is more chemically active than native ochres, and needs to be cautiously employed with pigments affected by iron, such as the lakes of cochineal and intense blue.

160. MIXED ORANGE.

Orange being a compound colour, the place of original orange pigments can be supplied by mixtures of yellow and red; either by glazing one over the other, by stippling, or by other modes of breaking and intermixing them, according to the nature of the work and the effect required. For reasons lately given, mixed pigments are apt to be inferior to the simple or homogeneous both in colour, working, and other properties; yet some pigments mix and combine more cordially and with better results than others; as is the case with liquid rubiate and gamboge. Generally speaking, the compounding of colours is easier in oil than in water; but in both vehicles trouble will be saved by beginning with the predominating colour, and adding the other or others to it.

Perhaps in this, our first chapter on the secondary colours, and consequently on colours that can be compounded, a few remarks on mixed tints from a chemical point of view will not be deemed superfluous.

There are two ways, we take it, of looking at a picture—from a purely chemical, and from a purely artistic, point of view. Regarded in the first light, it matters little whether a painting be a work of genius or a daub, provided the pigments employed on it are good and properly compounded. The effects produced are lost sight of in a consideration of the materials, their permanence, fugacity, and conduct towards each other. Painting is essentially a chemical operation: with his pigments for reagents, the artist unwittingly performs reaction after reaction, not with the immediate results indeed of the chemist in his laboratory, but often as surely. As colour is added to colour, and mixture to mixture, acid meets alkali, metal animal, mineral vegetable, inorganic organic. With so close a union of opposite and opposing elements, the wonder is not so much that pictures sometimes perish, but that they ever live. It behoves the artist, then, not only to procure the best and most permanent pigments possible, but to compound them in such a manner that his mixed tints may be durable as well as beautiful. To effect or aid in effecting this, although he may not always be able to act upon them, the following axioms should be borne in mind:—

1. If they do not react on each other, a permanent pigment added to a permanent pigment yields a permanent mixture.

2. If they do react on each other, a permanent pigment added to a permanent pigment yields a semi-stable or fugitive mixture.

3. A permanent pigment added to a semi-stable pigment yields a semi-stable mixture.

4. A permanent pigment added to a fugitive pigment yields a fugitive mixture.

Consequently—

5. A permanent pigment may be rendered fugitive or semi-stable by improper compounding.

6. A semi-stable or fugitive pigment is not rendered durable by being compounded.

7. As a chain is only as strong as its weakest link, so a mixture is only as permanent as its least durable constituent.

To give illustrations—

1. Ultramarine added to Chinese white yields a permanent mixture.

2. Ultramarine added to an acid constant white yields a semi-stable or fugitive mixture.

3. Ultramarine added to Prussian blue yields a semi-stable mixture.

4. Ultramarine added to indigo yields a fugitive mixture.

Except in the second instance, where the blue is either partially or wholly destroyed—in time, be it remembered, not at once—according to the quantity and strength of the acid in the white, the ultramarine remains unchanged. Hence at first sight our third and fourth conclusions may appear wrong; inasmuch as, it may be argued, a blue mixture cannot be semi-stable or fugitive when blue is left. To this we reply, unless both constituents are fugitive, a mixture will always more or less possess colour; but, if even one constituent be semi-stable or fugitive, a mixture will slowly but surely lose the colour for which it was compounded, and be as a mixture semi-stable or fugitive.

It need hardly be observed that the number of permanent orange, green, and purple hues which the artist can compound, depends mainly on the number of permanent yellows, reds, and blues at his disposal. In mixed orange, therefore, a selection of durable yellows and reds is of the first importance. It should, however, be remarked that mixed orange, more sober and less decided, is obtainable by the use of citrine and russet; in the former of which yellow predominates, and in the latter, red: consequently orange results when yellow is added to russet, red to citrine, or citrine to russet.

PERMANENT YELLOWS. PERMANENT REDS. Aureolin. Cadmium Red. Cadmium, deep. Liquid Rubiate. Cadmium, pale. Madder Carmine. Lemon Yellow. Rose Madder. Mars Yellow. Mars Red. Naples Yellow, modern. Ochres. Ochres. Vermilions. Orient Yellow. Raw Sienna.

None of these pigments react on each other, and from them can be produced the most durable mixed orange that yellow and red will afford.

161. NEUTRAL ORANGE,

or Penley's Neutral Orange, is a permanent compound pigment composed of yellow ochre and the russet-marrone known as brown madder: it is chiefly valuable in water-colour. Paper, being white, is too opaque to paint upon, without some wash of colour being first passed over it; otherwise the light tones of the sky are apt to look crude and harsh. It must, therefore, be gone over with some desirable tint, that shall break, in a slight degree, the extreme brilliancy of the mere paper. For this purpose, a thin wash of the orange is to be put over the whole surface of the paper with a large flat brush, care being taken never to drive the colour too bare, i.e. never to empty the brush too closely, but always to replenish before more is actually required. This first wash of colour not only gives a tone to the paper, but secures the pencil sketch from being rubbed out.

The reason why, in this compound, yellow ochre, as a yellow, is preferred to any of the others, is, that it is a broken yellow, that is, a yellow slightly altered by having another hue, such as red, or brown, in its composition. It is somewhat opaque too, and hence, from this quality, is especially adapted for distances. Brown madder also is a subdued red, which, when in combination with the former, produces a neutral orange, partaking of the character of soft light. As a general rule, yellow ochre is to predominate in broad daylight, and brown madder in that which is more sombre and imperfect: hence the pigment can be yellowed or reddened, by the addition of one or the other. For a clear sunset, the neutral orange must be repeated, with a preponderance of ochre at the top, assisted by a little cadmium yellow near the sun; the madder being added downwards.

In treating of distant mountains, a distinction is to be made between them and the clouds, the former requiring solidity, while the latter are only to be regarded as vapour and air. Mountains, being opaque bodies, are acted upon by atmosphere more or less, according to their position, their distance, and the state of the weather. To express this distinction, recourse must be had to an under tint, except where the tone is decidedly blue—an uncommon case. No mixture can give this with such truth as the neutral orange. A wash, therefore, should be passed over the mountains, with nearly all yellow in the high lights, or in the gleams of sunshine, and, on the contrary, almost all brown madder for the shadows. These two degrees of tone must be run into each other while the drawing is wet. A beautiful and soft under tone will thus be given to receive the greys.

162. ORANGE, OR BURNT ROMAN OCHRE,

called also Spanish Ochre, is a very bright yellow or Roman ochre burnt, by which operation it acquires warmth, colour, transparency, and depth. Moderately bright, it forms good flesh tints with white, dries and works well both in water and oil, and is a very good and eligible pigment. It may be used in enamel painting, and has all the properties of its original ochre in other respects.

A redder hue is imparted by mixing the ochre with powdered nitre before ignition, the orange red being subsequently washed with hot water.

* * * * *

163. Anotta,

Annotto, Annatto, Arnotto, Arnotta, Terra Orellana, Rocou, &c., is met with in commerce under the names of cake anotta, and flag or roll anotta. The former, which comes almost exclusively from Cayenne, should be of a bright yellow colour: the latter, which is imported from the Brazils, is brown outside and red within. It is prepared from the pods of the bixa orellana, and appears generally to contain two colouring matters, a yellow and a red, which are apt to adhere to each other and produce orange. Anotta dissolves with difficulty in water, but readily in alcohol and alkaline solutions, from which last it may be thrown down as a lake by means of alum. Being, however, exceedingly fugitive and changeable, it is not fit for painting; but is chiefly employed in dyeing silk, and colouring varnishes and cheese. Very red cheese should be looked upon with suspicion, for although the admixture of anotta is in no way detrimental to health provided the drug be pure, it is commonly adulterated with red lead and ochre. Several instances are on record that Gloucester and other cheeses have been found contaminated with red lead, through having been coloured with anotta containing it, and that this contamination has produced serious consequences.

Bixine is a purified extract of anotta made in France, and used by dyers.

164. Antimony Orange,

Golden Sulphur of Antimony, or Golden Yellow, is a hydro-sulphuret of antimony of an orange colour, which is destroyed by the action of strong light. It is a bad dryer in oil, injurious to many pigments, and in no respect eligible either in water or oil.

165. Chromate of Mercury

has been improperly classed as a red with vermilion, for though it is of a bright ochrous red in powder, when ground it becomes a bright ochre-orange, and affords with white very pure orange tints. Nevertheless it is a bad pigment, since light soon changes it to a deep russet colour, and foul air reduces it to extreme blackness.

166. Damonico,

or Monicon, is an iron ochre, being a compound of raw Sienna and Roman ochre burnt, and having all their qualities. It is rather more russet in hue than the pigment known as orange or burnt Roman ochre, has considerable transparency, is rich and durable in colour, and furnishes good flesh tints. As in orange ochre, powdered nitre may be employed in its preparation. Notwithstanding its merits, it is obsolete or nearly so; doubtless because burnt Sienna mixed with burnt Roman ochre sufficiently answers the purpose.

167. Gamboge Orange.

On adding acetate of lead to a potash solution of gamboge, a rich bright orange is precipitated, which may be washed on a filter till the washings are colourless, and preserves its hue with careful drying. The orange which we thus obtained stood well in a book, but it cannot be recommended as an artistic pigment. Perhaps in dyeing, the lead and gamboge solutions might be worth a trial.

168. Laque Minrale

is a French pigment, a species of chromic orange, similar to the orange chromate of lead. This name is likewise given to orange oxide of iron.

169. Madder Orange,

or Orange Lake. It has been said that the yellows so-called produced from madder are not remarkable for stability, differing therein from the reds, purples, russets, and browns. Like them, this 'orange' is of doubtful colour and permanence, and not to be met with, brilliant and pure, on the palette of to-day. The russet known as Rubens' madder has a tendency to orange.

170. Orange Lead,

of a dull orange colour, is an orange protoxide of lead or massicot. Like litharge, it may be employed in the preparation of drying oils, and, being a better drier than white lead, may be substituted for it in mixing with pigments which need a siccative, as the bituminous earths.

Minium sometimes leans to orange; and there is made from ceruse a peculiar red, Mineral Orange.

Orange Orpiment,

or Realgar, has also been called Red Orpiment, improperly, since it is a brilliant orange, inclining to yellow. There are two kinds, a native and an artificial, of which the former is the sandarac of the ancients, and is rather redder than the latter. They possess the same qualities as pigments, and as such resemble yellow orpiment, to which the old painters gave the orange hue by heat, naming it alchemy and burnt orpiment. Orange orpiment contains more arsenic and less sulphur than the yellow, and is of course highly poisonous. It is often sophisticated with brickdust and yellow ochre.

172. Thallium Orange

is produced when bichromate of potash is added to a neutral salt of the protoxide of thallium, as an orange-yellow precipitate. The scarcity of the metal precludes their present introduction as pigments, but if the chromates of thallium were found to resist the action of light and air, and not to become green by deoxidation of the chromic acid, they might possibly prove fitted for the palette. It is a question whether their very slight solubility in water would be a fatal objection; and, although they would be liable to suffer from a foul atmosphere, we are inclined to think the effects would not be so lasting as in the chromates of lead. Like lead sulphide, the sulphide of thallium ranges from brown to brownish-black, or grey-black; and, like it too, is subject to oxidation and consequent conversion into colourless sulphate. It is, however, much more readily oxidized than sulphate of lead; and hence the thallium chromates would doubtless soon regain their former hue on exposure to a strong light.

Mr. Crookes, who discovered this new metal in 1861, believes that the deep orange shade observable in some specimens of sulphide of cadmium is due to the presence of thallium. He has frequently found it, he says, in the dark-coloured varieties, and considers the variations of colour in cadmium sulphide to be owing to traces of thallium. That thallium affects the colour is most probable, but it is not necessarily the cause of the orange hue. The tint of cadmium sulphide is a mere matter of manufacture, seeing that from the same sample of metal there can be obtained lemon-yellow, pale yellow, deep yellow, orange-yellow, and orange-red. With deference to the opinion of a chemist so distinguished, we hold that thallium rather impairs the beauty of cadmium sulphide than imparts to it an orange shade, the thallium being likewise in the form of sulphide, and therefore more or less black. On chromate of cadmium, made with bichromate of potash, thallium would naturally confer an orange hue.

173. Uranium Orange

is obtainable by wet and dry methods as a yellowish-red, or, when reduced to powder, an orange-yellow, uranate of baryta. It is an expensive preparation, superfluous as a pigment.

174. Zinc Orange.

When hydrochloric acid and zinc are made to act on nitro-prusside of sodium, a corresponding zinc compound is formed of a deep orange colour, slightly soluble in water, and not permanent.

* * * * *

For a secondary colour, orange is well represented on the modern palette, and can point to some pigments as good and durable as any to be found among the primaries. Burnt Sienna, cadmium orange, Mars orange, neutral orange, and orange or burnt Roman ochre, are all strictly permanent. The so-called orange vermilions were, it will be remembered, classed among the reds.

As semi-stable, must be ranked chrome orange; and as fugitive, Chinese orange, orange orpiment, and orange lead.

From the foregoing division, the predominance of eligible orange pigments over those less trustworthy is manifest. Unfortunately, with many painters it is not so manifest that their secondary and compound colours should receive as much attention as the primaries, and that it is their duty, not only to the art which they practice, but to the patrons for whom they practice it, that their orange and green and purple hues, should be as durable as their yellows, reds, and blues. For such, the introduction of a new permanent pigment is of little interest, unless its colour be primary; so wedded are they to that passion for compounding which the chemist views with dismay. With dismay, because he knows that the rules of mixture are severe, and cannot with impunity be altered; that, although disguised in oil or gum, each pigment is a chemical compound, with more or less of affinity and power, more or less likely to act or be acted upon. Because he knows that, except with the most experienced artists, compounding leads to confusion; and that in it the temptations to use semi-stable or fugitive colours are strong. Look at those tables of mixed tints of which artist-authors are so fond, and tell us whether they always bear scrutiny—surely not. Admirable, perfect as these tints may be in an artistic sense, how often is their beauty like the hectic flush of consumption, which carries with it the seeds of a certain death. Will that orange where Indian yellow figures ever see old age, or that green with indigo, or purple with cochineal lake? Will they not rather spread over the picture the Upas-tree of fugacity, and kill it as they die themselves!



CHAPTER XII.

ON THE SECONDARY, GREEN.

Green, which occupies the middle station in the natural scale of colours and in relation to light and shade, is the second of the secondary colours. It is composed of the extreme primaries, yellow and blue, and is most perfect in hue when constituted in the proportions of three of yellow to eight of blue of equal intensities; because such a green will exactly neutralize and contrast a perfect red in the ratio of eleven to five, either of space or power. Of all compound colours, green is the most effective, distinct, and striking, causing surprise and delight when first produced by a mixture of blue and yellow, so dissimilar to its constituents does it appear to the untutored eye. Compounded with orange, green converts it into the one extreme tertiary citrine; while mixed with purple, it becomes the other extreme tertiary olive: hence its relations and accordances are more general, and its contrasts more agreeable with all colours, than those of any other individual colour. Accordingly it has been adopted very wisely in nature as the common garb of the vegetal creation. It is, indeed, in every respect a central or medial colour, being the contrast, compensatory in the proportion of eleven to five, of the middle primary red, on the one hand, and of the middle tertiary russet, on the other; while, unlike the other secondaries, all its hues, whether tending to blue or yellow, are of the same denomination.

These attributes of green, which render it so universally effective in contrasting colours, cause it also to become the least useful in compounding them, and the most apt to defile other colours in mixture. Nevertheless it forms valuable semi-neutrals of the olive class with black, for of such subdued tones are those greens by which the more vivid tints of nature are opposed. Accordingly, the various greens of foliage are always more or less semi-neutral in hue. As green is the most general colour of vegetal nature and principal in foliage; so red, its harmonizing colour, with compounds of red, is most general and principal in flowers. Purple flowers are commonly contrasted with centres or variegations of bright yellow, as blue flowers are with like relievings of orange; and there is a prevailing hue, or character, in the green colour of the foliage of almost every plant, by which it is harmonized with the colours of its flowers.

The chief discord of green is blue; and when they approximate or accompany each other, they require to be resolved by the opposition of warm colours. It is in this way that the warmth of distance and the horizon reconciles the azure of the sky with the greenness of a landscape. Its less powerful discord is yellow, which needs to be similarly resolved by a purple-red, or its principles. In tone, green is cool or warm, sedate or gay, either as it inclines to blue or to yellow; yet in its general effects it is cool, calm, temperate, and refreshing. Having little power in reflecting light, it is a retiring colour, and readily subdued by distance: for the same reason, it excites the retina less than most colours, and is cool and grateful to the eye. As a colour individually, green is eminently beautiful and agreeable, but it is more particularly so when contrasted by its compensating colour, red, as it often is in nature, even in the green leaves and young shoots of plants and trees. "The autumn only is called the painter's season," remarks Constable, "from the great richness of the colours of the dead and decaying foliage, and the peculiar tone and beauty of the skies; but the spring has, perhaps, more than an equal claim to his notice and admiration, and from causes not wholly dissimilar,—the great variety of tints and colours of the living foliage, accompanied by their flowers and blossoms. The beautiful and tender hues of the young leaves and buds are rendered more lovely by being contrasted, as they now are, with the sober russet browns of the stems from which they shoot, and which still show the drear remains of the season that is past."

The number of pigments of any colour is in general proportioned to its importance; hence the variety of greens is very great, though the classes of those in common use are not very numerous. Of the three secondaries, green is the colour most often met with, and, consequently, the most often compounded: for this last reason, perhaps, the palette is somewhat deficient in really good original greens—more deficient than there is any necessity for.

CHROME OXIDES.

By numerous methods both wet and dry, oxides of chromium are obtainable pale and deep, bright and subdued, warm and cool, opaque and transparent: sometimes hydrated, in which case they cannot be employed in enamelling; and sometimes anhydrous, when they are admissible therein. But whatever their properties may be, chemical, physical, or artistic, they are all strictly stable. Neither giving nor receiving injury by admixture, equally unaffected by foul gas and exposure to light, air, or damp, these oxides are perfectly unexceptionable in every respect. For the most part they are eligible in water and oil, drying well in the latter vehicle, and requiring in the former much gum. They have long been known as affording pure, natural, and durable tints; but, until within the last few years, have been rather fine than brilliant greens. Lately, however, processes have been devised, yielding them almost as bright, rich, and transparent, as the carmine of cochineal itself.

175. OXIDE OF CHROMIUM,

Opaque Oxide of Chromium, Green Oxide of Chromium, Chrome Oxide, True Chrome Green, Native Green, &c., is found native in an impure state as Chrome Ochre, but is always artificially prepared for artistic use. Obtained anhydrous by dry modes, this is the only chrome oxide available in enamelling, and is the one seen on superior porcelain. It is a cold, sober sage green, deep-toned, opaque, and, although dull, agreeable to the eye. Its tints with white are peculiarly delicate and pleasing, possessing a silvery luminous quality, and giving the effect of atmosphere. Being very dense and powerful, it must be employed with care to avoid heaviness, and is preferably diluted with a large quantity of white, or compounded with transparent yellow. In the hands of a master, this gray-green furnishes lustrous hues with brown pink, Italian pink, and Indian yellow; three beautiful but fugitive pigments, of which the two last may be replaced by aureolin. Of this Mr. Penley observes, "as adapted for the colouring of foliage and herbage, it is impossible to say too much in its praise. It imparts the vividness and freshness of nature to every colour with which it is combined;" and he brackets oxide of chromium with aureolin as a compound hue "extremely useful." In flat tints, the oxide sometimes does not wash well in water.

176. TRANSPARENT OXIDE OF CHROMIUM

being deficient in body, is only eligible in oil. A very pale greyish-white green in powder, it gives an agreeable yellowish green of some depth in oil, moderately bright, but not very pure or clear.

We are acquainted with another transparent chrome oxide of far greater beauty, brightness, purity, and clearness than the above. Of a bluish green hue, a difficulty in getting it to mix with oil renders it at present unavailable.

177. VERONESE GREEN,

or French Veronese Green, is a comparatively recent introduction, similar in colour and general properties to the following; beside which, however, it appears dull, muddy, and impure. It is often adulterated with arsenic to an enormous extent, which interferes with its transparency, mars its beauty, and renders it of course rankly poisonous.

178. VIRIDIAN

is a still later addition to the palette, and the only permanent green which can be described as gorgeous, being not unlike the richest velvet. Pure and clear as the emerald, it may be called the Prussian Blue of Greens, of such richness, depth, and transparency is it. In hue of a bluish-green, its deepest shades verge on black, while its light tints are marked by transparent clearness unsurpassed. No compound of blue and yellow will afford a green at once so beautiful and stable, so gifted with the quality of light, and therefore so suited for aerial and liquid effects. Used with aureolin, it gives foliage greens sparkling with sunshine; and, fitly compounded, will be found invaluable for the glassy liquidity of seas, in painting which it becomes incumbent to employ pigments more or less transparent. "The general failing in the representation of the sea is, that instead of appearing liquid and thin, it is made to bear the semblance of opacity and solidity. In order to convey the idea of transparency, some object is often placed floating on the wave, so as to give reflection; and it is strange that we find our greatest men having recourse to this stratagem. To say it is not true in all cases, is saying too much; but this we do assert, that as a general principle it is quite false, and we prove it in this way: water has its motion, more or less, from the power of the wind; it is acted upon in the mass, and thus divided into separate waves, and these individually have their surface ruffled, which renders them incapable of receiving reflection. The exception to this will be, where the heaving of the sea is the result of some gone-by storm, when the wind is hushed, and the surface becomes bright and glassy. In this state, reflections are distinctly seen. Another exception will be in the hollow portion of the waves, as they curl over, and dash upon the shore."

As viridian, like the sea, is naturally "liquid and thin, bright and glassy," the extract we have quoted from Mr. Penley, points to this green as a pigment peculiarly adapted for marine painting; in which, it may be added, its perfect permanence and transparency will be appreciated in glazing. Its fitness for foliage has been remarked; but in draperies the colour will prove equally useful, and in illumination will be found unrivalled. In the last branch of art, indeed, viridian stands alone, not only through its soft rich brilliancy, but by the glowing contrast it presents with other colours: employed as a ground, it throws up the reds, &c., opposed to it, in a marvellous manner. Like the three preceding oxides of chromium, viridian neither injures nor is injured by other pigments; is unaffected by light, damp, or impure air; and is admissible in fresco. In enamelling it cannot be used; the colour, depending on the water of hydration, being destroyed by a strong heat.

COPPER GREENS

are commercially known as Emerald Green, Malachite Green, Scheele's Green, Schweinfurt Green, Verdigris, Green Bice, Green Verditer, Brunswick Green, Vienna Green, Hungary Green, Green Lake, Mineral Green, Patent Green, Mountain Green, Marine Green, Saxon Green, French Green, African Green, Persian Green, Swedish Green, Olympian Green, Imperial Green, Mitis Green, Pickle Green, &c.

The general characteristics of these greens are brightness of colour, well suited to the purposes of house-painting, but seldom adapted to the modesty of nature in fine art; considerable permanence, except when exposed to the action of damp and impure air, which ultimately blacken most of them; and good body. They have a tendency to darken by time, dry well as a rule in oil, and are all more or less poisonous, even those not containing arsenic.

179. EMERALD GREEN,

Schweinfurt Green, Vienna Green, Imperial Green, Brunswick Green, Mitis Green, &c., is a cupric aceto-arsenite, prepared on the large scale by mixing arsenious acid with acetate of copper and water. It differs from Scheele's Green, or cupric arsenite, in being lighter, more vivid, and more opaque. Powerfully reflective of light, it is perhaps the most durable pigment of its class, not sensibly affected by damp nor by that amount of impure air to which pictures are usually subject: indeed it may be ranked as permanent both in itself and when in tint with white. It works better in water than in oil, in which latter vehicle it dries with difficulty. Bearing the same relation to greens generally as Pure Scarlet bears to reds, its vivid hue is almost beyond the scale of other bright pigments, and immediately attracts the eye to any part of a painting in which it may be employed. Too violent in colour to be of much service, it has the effect, when properly placed, of toning down at once, by force of contrast, all the other greens in a picture. If discreetly used, it is occasionally of value in the drapery of a foreground figure, where a bright green may be demanded; or in a touch on a gaily painted boat or barge. When required, no mixture will serve as a substitute. Compounded with aureolin, it becomes softened and semi-transparent, yielding spring tints of extreme brilliancy and beauty.

180. SCHEELE'S GREEN,

or Swedish Green, resembles the preceding variety in being a compound of copper and arsenic, and therefore rankly poisonous; but differs from it in containing no acetic acid, in possessing less opacity, and in having a darker shade. It is a cupric arsenite, with the common attributes of emerald green, under which name it is sometimes sold. Of similar stability, it must not be employed with the true Naples yellow or antimoniate of lead, by which it is soon destroyed.

Upon the lavish use of this dangerous pigment in colouring toys, dresses, paper-hangings, artificial leaves, and even cheap confectionery, it is not our province to enlarge: the constant-recurring diseases and deaths, which, directly or indirectly, result from the employment of arsenical pigments, are such every-day facts that they are merely deplored and forgotten. With arsenic on our heads, our clothes, our papers, our sweets, our children's playthings, we are so accustomed to live—and die—in a world of poison, that familiarity with it has bred contempt. Into the fatal popularity, therefore, of arsenical colours for decorative purposes, we shall not further enter; but it behoves us to deprecate their presence, and the presence of all poisonous pigments, in colour-boxes for the young. It is one of the pleasures of childhood to suck anything attractive that comes in its way, openly if allowed, furtively otherwise: and as in early life we have a preference for brilliancy, so vivid a pigment as Scheele's green is an object of special attention. Artistically, it matters little whether a pigment is noxious or not, but we hold that poison should not be put into the hands of the young; and indeed are of opinion that a box of colours is about the worst present a child can receive.

181. MALACHITE GREEN,

or Mountain Green, is met with in Cumberland, and is also found in the mountains of Kernhausen, whence it is sometimes called Hungary Green. It is prepared from malachite, a beautiful copper ore employed by jewellers, and is a hydrated dicarbonate of copper, combined with a white earth, and often striated with veins of mountain blue, to which it bears the same relation that green verditer bears to blue verditer. The colour, which may be extracted from the stone by the process followed for native ultramarine, varies from emerald-green to grass-green, and inclines to grey. It has been held in great esteem by some, and considered strictly stable, on the assumption, probably, that a pigment obtained from a stone like ultramarine, and by the same method, could not be otherwise than permanent. That it is so, with respect to light and air, there is no denying; but the green, when separated from the ore and purified for artistic use, is merely a carbonate of copper, and therefore subject to the influence of damp and impure air, in common with other non-arsenical copper colours. As a pigment, native malachite green has the same composition, or very nearly the same, as that which can be artificially produced, and answers to the same tests. Water-rubs of the two varieties which we exposed to an atmosphere of sulphuretted hydrogen became equally blackened by the gas. Practically, there is little or no difference between them: both preserve their colour if kept from damp and foul air, both are injured by those agents, and both are liable to darken in time, especially when secluded from light. The artificial, however, can be obtained of a much finer colour than the natural, which it may be made to resemble by admixture with mineral gray. On the whole, they can scarcely be recommended for the palette, and are certainly inferior in durability to Scheele's and Schweinfurt greens. In fresco painting they have been pronounced admissible; but, apart from the question of damp, we should deem the conjunction of lime with carbonate of copper not favourable to permanence. By the action of alkalies, even the native green malachite may be converted into blue; and it becomes a question whether the dingy greenish-blue on some ancient monuments was not originally malachite green.

182. VERDIGRIS,

or Viride ris, is of two kinds, common or impure, and crystallized or Distilled Verdigris, or, more properly, refined verdigris. The best is made at Montpellier in France, and is a sub-acetate of copper of a bright green colour inclining to blue. The least durable of the copper greens, it soon fades as a water-colour by the action of light, &c., and becomes first white and ultimately black by damp and foul gas. In oil, verdigris is permanent with respect to light and air, but moisture and an impure atmosphere change its colour, and cause it to effloresce or rise to the surface through the oil. It dries rapidly, and is exceptionally useful with other greens or very dark colours. In varnish it stands better; but cannot be considered safe or eligible, either alone or compounded. Vinegar dissolves it, forming a solution used for tinting maps, and formerly much employed for colouring pickles, &c.

The painters, who lived at the time when the arts were restored in Italy, used this pigment; and the bright greens seen in some old pictures are made by glazings of verdigris. It is often largely adulterated with chalk and sulphate of copper.

183. MIXED GREEN

Green, being a compound of blue and yellow, may be got by combining those colours in the several ways of working—by mixing, glazing, hatching, or otherwise blending them in the proportions of the various hues required. To obtain a pure green, which consists of blue and yellow only, a blue should be chosen tinged with yellow rather than with red, and a yellow tinged with blue. If either a blue or a yellow were taken, tinged with red, this latter colour would go to produce some grey in the compound, which would tarnish the green. The fine nature-like greens, which have lasted so well in some of the pictures of the Italian schools, appear to have been compounded of ultramarine, or ultramarine ashes and yellow. Whatever pigments are employed on a painting in the warm yellow hues of the foreground, and blue colouring of the distance and sky, are advantageous for forming the greens in landscape, &c., because they harmonize better both in colouring and chemically, and impart homogeneity to the whole: a principle conducive to a fine tone and durability of effect, and applicable to all mixed tints. In compounding colours, it is desirable not only that they should agree chemically, but that they should have, as far as possible, the same degree of durability. In these respects, aureolin and ultramarine, gamboge and Prussian blue, Indian yellow and indigo, are all judicious mixtures, although not all to be recommended.

PERMANENT YELLOWS. PERMANENT BLUES. Aureolin. Cerulian Blue. Cadmium Yellow, pale. Cobalt Blue. Cadmium Yellow, deep. Genuine Ultramarine. Lemon Yellow. Brilliant Ultramarine. Mars Yellow. French Ultramarine. Naples Yellow, modern. New Blue. Ochres. Permanent Blue. Orient Yellow. Raw Sienna.

The foregoing yellows and blues are in no wise inimical to each other, and yield the best mixed greens, chemically considered, the palette can afford. In an artistic sense, we confess, the result is not so satisfactory: the list of blues, it must be admitted, being somewhat scant. Among the latter there is no pigment with the wonderful depth, richness, and transparency of Prussian blue, and none consequently which will furnish with yellow a green of similar quality. That the artist, therefore, will dispense with Prussian blue, it would be too much to expect. There is, however, less necessity for it since the introduction of viridian, a green resembling that which is produced by admixture of Prussian blue and yellow, and which may be varied in hue by being compounded with aureolin or ultramarine. Our object in this work is to give precedence to the chemical rather than the artistic properties of pigments, to separate the strictly stable from the semi-stable, and the semi-stable from the fugitive. A colour or a mixture may be chemically bad but artistically good, and vice vers; but the chemist looks upon no pigment or compound with favour unless it be perfectly permanent, and ignores its mere beauty when void of durability. Hence, all artistic considerations are set aside in our lists of permanent pigments: if it be possible to use them alone, so much the better for the permanence of painting; if not, so much the worse will it be, according to the degree of fugacity of the colours employed.

184. BRONZE,

and the three succeeding varieties, are greens resembling each other in being semi-stable, and more or less transparent. Bronze is a species of Prussian green, of a dull blue-black hue. In its deep washes it appears a greenish-black with a coppery cast. It is used in ornamental work, and sometimes as a background tint for flower pieces.

185. CHROME GREENS,

commonly so called, are compounds of chromate of lead and Prussian blue, a mixture which is also known as Brunswick Green. Fine bright greens, they are suited to the ordinary purposes of mechanic painting, but are quite unfit for the artist's craft, chrome yellow reacting upon and ultimately destroying Prussian blue when mixed therewith. For the latter, cheap cobalts and ultramarines are preferably substituted, although they do not yield greens of like power and intensity.