Aureolin.	Aureolin.	Aureolin.	Aureolin.
Burnt Sienna.	Vandyke Brown.	Sepia.	Sepia, or Rose Madder.
Indigo, or French Blue.	Indigo, or French Blue.		Cobalt.
Aureolin.	Aureolin.	Aureolin.	Aureolin.
Indigo.	Oxide of Chromium.	Emerald Green.	Light Red.
			Cobalt, or Indigo.
Aureolin.	Aureolin.	Aureolin.	Aureolin.
Burnt Sienna.	Burnt Umber.	Brown Madder.	Rose Madder.

The foregoing sufficiently proves the value of aureolin in water, and similar flattering notices have been given of the colour in oil. Both in a chemical and artistic sense, therefore, this new primitive yellow merits the highest regard, and justly claims a foremost place among that little band of pigments which are without fear and without reproach.

For mural decoration, aureolin is admirably adapted, but it cannot be used in enamel, the colour being destroyed by great heat.

CADMIUM YELLOWS.

Of these there are three tints, Deep, a so-called Pale, and Lemon.

21. DEEP CADMIUM.

Cadmium Yellow is comparatively a recent introduction, the metal itself not having been discovered till 1818. The cadmium yellows of commerce are (the chromate excepted) all sulphides, and therefore not affected by impure air. Until lately, they were not manufactured in England but imported from abroad, and as a rule were sadly doctored. We have found in them a large proportion of orpiment, chromate of lead, &c., together with quantities of soluble salt, extracted by boiling water. Owing to careless preparation, there was also present an unnecessary amount of dirt, which interfered as much with the purity of the colour, as sophistication lessened its stability. For these reasons, doubtless, cadmium yellows got to be regarded by some with disfavour and suspicion; and it may fairly be said that they did not attain their present popularity, until they became an article of home produce.

Deep cadmium yellow, if genuine, may without hesitation be declared permanent, both with respect to foul gas, and exposure to light or air. The variety under notice is of extreme depth, inclining to orange, glowing, lustrous, and brilliant. It is not very transparent, but wonderfully clear and bright, of great power, and the most richly toned yellow known. For draperies it is particularly adapted, and for gorgeous sunsets is invaluable. It works and washes well, readily throws all other yellows into the shade when used alone, and combines admirably with Chinese white for the light touches of bright clouds or mountains.

By admixture with white, cadmium gives a series of beautiful clear tints. When compounded with white lead, however, the colour has been stated to be destroyed. Theoretically, this might very well happen. Cadmium yellow is composed of cadmium and sulphur—white lead of lead and carbonic acid. If the former parted with some of its sulphur to the latter, sulphide of lead would result, which is black. Hence, the partly decomposed yellow and white would be mixed with black, and there would be formed a blackish-yellow or a yellowish-black. Again, if the cadmium parted with the whole of its sulphur to the lead, receiving in exchange the carbonic acid of the latter, a mixture of black sulphide of lead with white carbonate of cadmium would be furnished, the result being a grey. Perhaps the following rough diagram may serve to make our meaning plainer:—

Cadmium Yellow

{

Cadmium. Sulphur.

admixture diagram

Carbonate of Cadmium (White.)

White Lead

{

Lead. Carbonic Acid.

Sulphide of Lead (Black.)

Such is the theory of the reaction which might take place, but which, as far as our own experience goes, does not. Some deep cadmium yellow which we ourselves prepared was intimately mixed and ground with an equal quantity by weight of Cremnitz white, and an oil rub of the compound laid upon a tile. Having placed the latter on a shelf in the laboratory, we watched from week to week to see if any approach to blackness occurred, any diminution in the beauty of the tint; but could perceive none. Hence, while admitting the possibility of the colour being damaged or destroyed in the case of an inferior and spurious article, we conclude that an unadulterated cadmium yellow, containing no free sulphur, neither injures, nor is injured by, white lead, and may safely be used therewith. At the same time, the artist should be warned to satisfy himself of the genuineness of his pigment, or otherwise to employ the white of zinc, at least as a medium of intervention.

A good sample of cadmium yellow may rather advantageously than otherwise be compounded with white lead, for we have found that a mixture of equal parts by weight of the two will bear an atmosphere of sulphuretted hydrogen that completely blackens the white alone.

With all the sulphides of cadmium a steel palette knife is best avoided.

22. PALE CADMIUM.

The cadmium yellow so-called, is not strictly pale, but pale only when compared with the preceding. It is, in fact, a full rich colour, brilliant and permanent, but without that tendency to orange which distinguishes the deep. For some purposes, when a warm tone is not required, such a tint is preferable. In water, especially, where delicacy of colouring can be carried to a greater degree of refinement than in oil, these differences of hue are important. In the first medium the faint washes show with a clearness which is not so apparent in the last, and the most subtle gradation of tone tells with a force in some measure lost in oil. As a consequence, the colour of the lightest tints in the distance must be as true as that of the deepest shades in the foreground, and hence the warmth or coldness of the pale washes of a pigment should be duly considered.

Pale cadmium yellow with or without aureolin, is adapted for golden sunsets, and yields with French blue a beautiful sea-green.

24. LEMON CADMIUM.

Very pale cadmium yellows are not permanent, and lemon cadmiums are decidedly fugitive. Being, like the deep and 'pale' varieties, sulphides, they are of course unaltered by sulphurous gas; but they will not stand exposure to light and air, or even to light alone. Some which were submitted in an air-tight bottle to the action of light gradually whitened next the glass. Yet they were almost identical in composition with the deepest and most orange hues, and might have reasonably been presumed stable. Repeated experiments, however, both with samples of our own making and of others' manufacture, have shown that for a cadmium to be durable, it must be of a full, rich, comparatively deep yellow; and that any paler product than the 'pale' alluded to cannot be depended on. It is true that a light or lemon tint will fade quicker in water than in oil, but a colour which is fugitive in the one vehicle cannot be regarded as eligible in the other. From a somewhat long acquaintance with cadmiums, we have derived the opinion that their stability rests much on the mode of preparation, and that an amount of heat is needed sufficient to make the sulphur bite into the base. This opinion, indeed, extends to all metallic sulphides, and our belief is, that if vermilions were made generally by wet processes, they would not be found the permanent pigments they undoubtedly are.

25. MUTRIE YELLOW.

Under this name a lemon sulphide of cadmium has lately appeared, to which the foregoing remarks are applicable. A water colour rub on exposure to air and light faded rapidly, no trace of yellow remaining in the pale wash. The sample which came under our notice contained a quantity of free sulphur.

It is to be regretted that these lemon cadmiums are fugacious, so bright, so clear, are they, and of so pure a lemon tint can they be obtained. But as no beauty of colour compensates for want of durability, their place should be supplied by lemon yellow proper, or chromate of baryta.

26. CHROME YELLOWS,

Also called Jaune MinÉrale, Jaune de Cologne or Cologne Yellow, Pale Chrome, and Deep Chrome, are chromates of lead, in which the latter metal more or less exists, according to the paleness or depth of the colour. Of modern introduction, they are distinguished for their brilliancy, their opacity and body, and their going cordially into tint with white, both in water and oil. Owing, however, to a harshness and hardness of tone for which they are peculiar, a coarse and disagreeable effect is apt to be produced by their use. In general, they do not accord with the modest hues of nature, nor harmonize well with the softer beauty of other colours. Rivalling the cadmiums in brightness, they are wanting in the mellow richness which belongs to the deeper varieties of those pigments, as well as in their permanency. Although they resist the sun's rays for a lengthened period, after some time they lose their original hue, whether employed alone or in tint, and may even become black in impure air. Upon several pigments they produce serious changes, ultimately destroying Prussian and Antwerp blues, when compounded therewith in the composition of greens, &c. Ranging from lemon to deep yellow, in oil, provided the atmosphere be good, the chromes may be found comparatively durable; but, on the whole, the artist cannot trust to them his reputation as a colourist.

The chromates are often mixed with sulphate of lead, as well as with the sulphates of baryta and lime. The presence of the first is especially objectionable, as increasing the tendency of the yellows to be blackened by foul gas. The sulphates of baryta and lime, however, are sometimes formed in the process of preparation, in which case they are rather an advantage than otherwise; inasmuch as they not only lend a softness to the colour, but decrease the proportion of leaden base, and consequently the tendency referred to. We may remark, indeed, with respect to pigments, that it is difficult in many instances to say where manufacture ends and adulteration begins. A substance may be present which, although not absolutely essential to the colour itself, has been legitimately employed to impart a desired quality, or a certain tint.

27. COLOGNE YELLOW

Is a cheap inferior chrome yellow, unfit for artistic purposes, and consists of twenty-five parts of chromate of lead, fifteen of sulphate of lead, and sixty of sulphate of lime.

28. JAUNE MINERALE

Is prepared in Paris, and differs in no essential particular from ordinary chromate of lead, except in the paleness of its colour. The chrome yellows have also obtained other names from places or persons, whence they have been brought or by whom they have been made. Another lead yellow, not a chromate, has likewise been called jaune minÉrale.

29. CITRON YELLOW

Is chromate of zinc, a bright pale lemon-like yellow, slightly soluble in water. It is not affected by foul gas, but does not preserve its colour on exposure to light and air, or even when kept in a book. In contact with organic substances it is apt to turn green. Compounded, especially for foliage tints, this yellow is eligible; but if purity of hue be desired, it should certainly not be employed alone. In this chromate, as in many others, the affinity of the chromic acid to the base is small; the former is liable to separate from the latter, and, by deoxidation, to become converted into green oxide of chromium.

30. GALLSTONE

Is a deep-toned gorgeous yellow, affording richer tints than most other yellows, but it cannot be depended on for permanency, and therefore is seldom employed. Its colour is soon changed and destroyed by strong light, though not subject to alteration by impure air. In oil it is ineligible. A true gallstone is an animal calculus formed in the gall-bladder, chiefly of oxen; but the pigment sold under that name is often replaced by a substitute, resembling the original in colour, but of greater stability.

31. GAMBOGE,

Sometimes designated Drop Gum, and variously written Gamboge, Camboge, Gamboage, Cambogia, Cambadium, Cambogium, Gambodium, Gambogium, &c., is the produce of several kinds of trees. The natives of the coast of Coromandel call the tree from which it is principally obtained Gokathu, which grows also in Ceylon and Siam. From the wounded leaves and young shoots the gamboge is collected in a liquid state and dried. Our indigenous herb Celandine yields abundantly, in the same manner, a beautiful yellow juice of the same properties as gamboge. Gamboge is of a gum-resinous nature and clear yellow colour. It is bright and transparent, but not of great depth, and in its deepest touches shines too much and verges upon brown. When properly used, it is more durable than generally reputed, both in water and oil; and conduces, when mixed with other colours, to their stability and keeping their place, on account of its gum and resin. It is deepened in some degree by ammoniacal and impure air, and somewhat weakened, but not easily discoloured, by the action of light. Time effects less change on this colour than on other bright vegetal yellows; but white lead and other metalline pigments injure, while terrene and alkaline substances redden it. In water it works remarkably well, and forms an opaque emulsion without grinding or preparation, by means of its natural gum; but is with difficulty employed in oil, &c., in a dry condition. It dries well, however, in its natural state, and lasts in glazing when deprived of its gum. With regard to other colours it is perfectly innocent, and though a strong medicine, is not dangerous or deleterious in use. Gamboge has been employed as a yellow lake, precipitated upon an aluminous base; but a better way of preparing it is to form a paste of the colour in water, and mix it with lemon yellow, with which pigment being diffused it goes readily into oil or varnish. Glazed over other colours in water, its resin acts as a varnish which protects them; and under other colours its gum acts as a preparation which admits varnishing. It is injured by a less degree of heat than most pigments.

In landscape, gamboge affords with indigo or Antwerp blue clear bright greens, and with sepia a very useful sober tint. For sunrise and sunset clouds, a mixture of gamboge and cadmium yellow will be found useful.

32. EXTRACT OF GAMBOGE

Is the colouring matter separated from its greenish gum and impurities by solution in alcohol, filtration and precipitation, by which it acquires a powdery texture, rendering it miscible in oil, &c., and capable of being employed in glazing. At the same time it is improved in colour, and retains its original property of working well in water with gum. Gamboge is likewise soluble in caustic potash, forming a red liquid, from which it is thrown down by acids.

33. INDIAN YELLOW

Is a pigment long employed in India under the name Purree, but has not many years been introduced generally into painting in Europe. It is imported in the form of balls of a fetid odour, and is produced from the urine of the camel. It appears to be a urio-phosphate of lime, and is of a beautiful pure yellow colour and light powdery texture; of greater body and depth than gamboge, but inferior in these respects to gallstone. Indian yellow resists the sun's rays with singular power in water painting; yet in ordinary light and air, or even in a book, the beauty of its colour is not lasting. In oil it is exceedingly fugitive, both alone and in tint. Owing probably to its alkaline nature, it has an injurious effect upon cochineal lakes and carmine when used with them. The colour is not damaged by foul air, and, as lime does not destroy it, the pigment may be employed in fresco according to its powers.Indian yellow washes and works extremely well, and is adapted for draperies and for compounding landscape greens—where permanency is not required. Blackness in the darkest shadows of the foliage will sometimes result from too great a use of indigo; should this evil exist, no colour is so fitted to regain the proper tone as Indian yellow employed thickly.

LAKES.

There are several pigments of this denomination, varying in colour and appearance according to the substances used and modes of preparation. Usually they are in the form of drops, and their colours are in general bright yellow, very transparent, and not liable to change in an impure atmosphere—qualities which would render them very valuable, were they not soon discoloured and even destroyed on exposure to air and light, both in water and oil. In the latter vehicle, they are bad driers, like most lakes, and they do not stand the action of white lead and other metallic pigments. If used, therefore, it should be as simple as possible. Of these lakes, the following are the best; but it must be borne in mind that, as not one of them is permanent, the compounds they afford are of necessity unstable.

34. YELLOW LAKE

Is a bright transparent yellow, a difficult drier, and liable to be destroyed by light. It affords beautiful foliage tints, and would, if it could be depended on, be of extreme value in what is called "glazing."

35. ITALIAN PINK,

Also called English and Dutch Pink, is an absurd name for a stronger and richer kind of yellow lake, warmer in tint and more powerful than the preceding. It is a rich transparent yellow, yielding a variety of fine foliage tints by admixture with indigo and sepia in different proportions. These three colours with burnt sienna will produce almost every variety of sunny foliage. It gives likewise good olive greens with lamp black.

36. QUERCITRON LAKE,

Or Quercitron Yellow, is what its name implies. It is dark in substance, in grains of a glossy fracture, perfectly transparent, and when ground is of a beautiful yellow colour. In painting it follows, and adds richness and depth to, gamboge in water, and goes well into varnish; but any lead used in rendering oils siccative, browns it, and for the same reason it is useless in tints.

37. LEMON YELLOW,

Or chromate of baryta, is exceedingly difficult to make well. Upon the mode of manufacture depend not only the beauty of the colour but its stability. If properly and carefully prepared, it is of a vivid lemon tint, deep or pale, very clear, very pure and permanent. It also washes well, and is entirely free from the slightest tinge of orange. This may be pronounced the only chromate which possesses durability, not being liable to change by damp or foul air, by the action of light or the steel palette-knife, or by mixture with white lead and other pigments, either in water or oil, in both of which it works pleasantly. Lemon yellow is chiefly adapted to points of high light, and has a peculiarly happy effect when glazed over greens in both modes of painting. In water it exceeds gamboge in brightness, and compounded therewith improves its beauty. This mixture also goes readily into oil; indeed it is the best and easiest way of rendering gamboge diffusible as an oil colour—simple emulsion of the gamboge in a little water, and trituration of the lemon yellow therewith, being all that is requisite for the purpose.

Lemon yellow has not much power, and is semi-opaque. In distance, its light wash is used with great effect for cool sunny greens, for which a minute quantity of emerald green may be added to it. Being uninjured by lime, the colour is eligible in fresco and crayons.

38. MARS YELLOW,

Jaune de Mars, Jaune de Fer, Iron Yellow, &c., is an artificially prepared iron ochre, of the nature of sienna earth. In its general qualities it resembles the ochres, with the same eligibilities and exceptions, but is more transparent, as well as purer, clearer, richer, and brighter. Like them it is quite permanent. The colours of iron exist in endless variety in nature, and are capable of the same variation by art, from sienna yellow, through orange and red, to a species of purple, brown, and black, among which are useful and valuable distinctions. They were formerly introduced by the author, and have been received under the names of Mars yellow, Mars orange, Mars red, Mars violet, and Mars brown. All of them are brighter and purer than native ochres, and equally stable. When carefully prepared, these pigments dry well in proportion to their depth, are marked by a subdued richness rather than brilliancy, and have the general habits of sienna earths and ochres. Their faint washes possess the desirable quality of transparent clearness.

We have occasionally found Mars yellow mixed with orpiment, or chromate of lead, for the purpose of brightening the colour.

39. NAPLES YELLOW

Was a compound of lead and antimony, anciently prepared at Naples under the name of Giallolino, and was variously of a pleasing light, warm yellow tint. It was opaque and of good body, not altered by the light of the sun, and might be used with comparative safety in oil or varnish, under the same management as the whites of lead. Like these, however, it was liable to change even to blackness by damp and impure air when employed in water. Iron was also destructive of the colour of this yellow, on which account great care was requisite, in grinding and using it, not to touch it with the common steel palette knife, but to compound its tints with a spatula of ivory or horn. For the same reason, it was apt to suffer in composition with ochres, Prussian and Antwerp blues, and other pigments of which iron was a principal or ingredient. Used pure or with white lead it was eligible in oil, in which it worked and dried well. It was also employed in enamel painting as it vitrified without change. In this state it was called Giallolino di fornace, and was introduced as a pigment for artists, under the erroneous conception that vitrification gives permanence to colours, when in truth it only increases the difficulty of levigation, and injures their texture for working. We have spoken of Naples yellow in the past tense, because the pigment now sold as such is generally, or always, a compound colour, or manufactured with a zinc instead of a lead base. In either case the preceding remarks are not applicable to the present product, which is perfectly durable and trustworthy. The new Naples yellow presents an example of an old objectionable pigment being replaced by a different and superior preparation. However fugitive certain colours may have been, the fact of their once having had a place on the palette would seem to be sufficient recommendation to some. At any rate, they are still in occasional request, and we cannot but approve the pious fraud which offers under the same name a good substitute for a bad original. If an artist must needs demand a worthless pigment, he had better buy a colour like it that will stand, even if it be not what he asked for.

The tints of Naples yellow are readily and accurately imitated by admixture of deep cadmium yellow and white.

40. ANTIMONY YELLOW,

As its name denotes, was likewise a preparation of that metal, of a deeper colour than Naples yellow, but similar in its properties. It was principally used in enamel and porcelain painting, and differed greatly in tint. One variety, brighter than the rest, is stated not to have been affected by foul air, and therefore could not have had a lead basis.

OCHRES,

Known as Yellow Ochre, Brown Ochre, Roman Ochre, Transparent Gold Ochre, Oxford Ochre, Stone Ochre, Di Palito, &c., are native earths, consisting chiefly of silica and alumina in combination with iron, which latter forms the principal colouring matter. They are among the most ancient of pigments, and their permanency is proved by the state of the old pictures. In a box of colours found at Pompeii, and analyzed by Count Chaptal, he discovered yellow ochre purified by washing, which had preserved its original freshness. They may all be produced artificially in endless variety as they exist in nature, and are all converted by burning into reds or reddish-browns. Several ochres are found in the natural state of so very fine a quality, that they require no other preparation than that of being washed. Their colours may be imitated to a certain extent by means of iron alone, uncombined with silica and alumina; but such ferruginous preparations are not equally durable, and as their chemical action is stronger, they are more likely to affect those pigments which are damaged by iron. It often happens in colours that one component of weak stability, or powerful for evil, is strengthened and held in check by another; thus in the case of the ochres, the silica and alumina by keeping a tight hand on the iron, both ensure its safety, and prevent it injuring others.

41. YELLOW OCHRE,

Called also Mineral Yellow, is found in most countries, and abundantly in our own. It differs much both in constitution and colour, ranging from a tolerably bright though not vivid yellow to a brown-yellow, and is generally of a warm cast. Its natural variety is much increased by artificial dressing and compounding. The best yellow ochres possess no great force, but as far as they go are valuable pigments, particularly in fresco and distemper, being neither subject to change by ordinary light, nor sensibly affected by impure air, or the action of lime. By time, however, and the direct rays of the sun, they are somewhat darkened. Like other ochres, they may be safely used in admixture with pigments which are themselves permanent. With carmine and the cochineal lakes, or intense blue, the ochres are best not employed.

The impunity with which yellow ochre bears foul gas is one of its many recommendations. No immediate effect whatever is produced by sulphuretted hydrogen, and only a slight dirty brown tint is imparted by its prolonged action. This discolouration a short exposure to air and light quickly removes. By keeping the ochre sufficiently long in contact with sulphide of ammonium a jet black is obtainable, but a rub of it in a moist unwashed state completely regains its yellow hue in a day or so. Hence, yellow ochre compounded with pigments which suffer from an impure atmosphere doubtless acts as a preservative agent.

Yellow ochre is usually employed in the distance and middle ground of a landscape. It possesses a slight degree of turbidness, and is esteemed for this property, which is considered to give it a retiring quality. By admixture with Antwerp blue or indigo it affords a fine range of quiet greens, also a very serviceable yellowish drab with Vandyke brown. The ochre is valuable in warm skies, the sails of ships and boats, sandstone rocks and cliffs, buildings, hay, sheep, &c. It does not compound kindly with any of the cold colours, and should therefore be used as a wash over others that are dry, when required to qualify their tints.

42. ROMAN OCHRE

Is rather deeper and more powerful than the preceding, as well as more transparent and cool in tint. In other respects it is similar, and forms with Antwerp blue and indigo a like excellent range of greens. We may observe, however, that as indigo is not a permanent pigment, the colours it yields by admixture cannot be durable as far as the blue is concerned. Roman ochre and brown madder are admirably adapted for red sails, and autumnal effects of foliage.

43. BROWN OCHRE,

Likewise known as Spruce Ochre and Ocre de Rue, or, more correctly Ru, is a dense, deep-toned brownish yellow, fine in sandy foregrounds. With Indian yellow it gives a dark autumnal tint of great richness, but stable only as respects the ochre. When mixed with other colours, it furnishes a series of rich yet sober tones of extensive use. It covers well, without being too opaque; and compounded with black and a little brown-red is good for backgrounds, &c.

44. TRANSPARENT GOLD OCHRE

Resembles in a great degree Roman ochre, but is clearer in its tints, and more transparent. It is also brighter and much less opaque than yellow ochre. It approaches somewhat the character of clear bright raw sienna, though more pure and brilliant, serving for strong semi-transparent greens and sunny effects.

45. OXFORD OCHRE

Is a native pigment from the neighbourhood of Oxford, semi-opaque, of a warm yellow colour and soft argillaceous texture, absorbent of water and oil, in both of which it may be safely employed. It is one of the best of yellow ochres.

46. STONE OCHRE

Has been confounded with the last variety, to which, as well as to Roman ochre, it is frequently similar. True stone ochres are found in balls or globular masses of various sizes in the solid body of stones, lying near the surface of rocks among the quarries of Gloucestershire and elsewhere. These balls are smooth and compact, in general free from grit, and of a powdery fracture. They vary exceedingly in colour, from yellow to brown, murrey, and gray, but otherwise do not differ from ordinary ochres.

In enamel they may be used for browns and dull reds.

47. DI PALITO

Is a light yellow ochre, with no special distinguishing quality, except that its tints are rather purer in colour than most ochres.

48. ORIENT YELLOW

Is an entirely new preparation of absolute permanence, and perfectly unexceptionable in all respects, both in water and oil. We can give it no higher praise than by saying it equals aureolin in stability, as well as in neither injuring, nor being injured by, other colours. Not possessed of the same amount of transparency, it is distinguished by greater richness and depth. Of a soft golden hue, lustrous and luminous, it resembles a brilliant and somewhat opaque Indian yellow. A gorgeous and durable substitute for that fugitive pigment is produced by compounding the orient with aureolin, or by using the latter as a glaze. Being more transparent than cadmiums and less obtrusive, the new yellow is adapted for mellow sunset and sunrise clouds, or for sunshine on distant mountains. With French blue it affords a beautiful sea green; and, mixed with aureolin, gives fine foliage tints. It is also eligible for draperies and illumination. For enamelling it is inadmissible, the colour being destroyed by great heat; but in fresco it may safely be employed.

As in the case of aureolin, we have had a prolonged personal experience of this new yellow, an experience which justifies us in asserting that there is none more permanent. In the whole range of artistic colours there is no pigment less affected by chemical or physical agents. Acid and ammoniacal fumes, foul gases, and exposure to damp, air, light, or sunshine, equally fail to injure it. The perfect impunity with which it bears the action both of sulphuretted hydrogen and sulphide of ammonium is remarkable. The former gas may be continuously passed into the colour suspended in water, or a strong solution of the latter sulphide be poured upon it, and the yellow remains unchanged. Submitted to the direct rays of the sun during an entire summer, its lightest and faintest tints have preserved their original hue.

In a preceding chapter we remarked that, provided the colour be stable, the more colour a pigment possesses the better. The "latent colour" there alluded to, is one of the advantages of orient yellow. The more it is looked into, the more colour is seen—there is no suspicion of a base coloured, the pigment is colour itself.

49. ORPIMENT,

Also called King's Yellow, Chinese Yellow, Yellow Orpiment, &c., was known in ancient times: the Romans called it auri pigmentum or gold colour, whence, by corruption, its present name is derived. It is found in the native state in China and elsewhere, the best quality being in masses, consisting of plates of a fine golden hue, intermixed with portions of a vermilion or orange-red colour; the inferior kinds are yellow or greenish yellow. Of orpiment, or sulphuret of arsenic, which is produced artificially, there are two distinct varieties; one of a bright pure yellow tint, in which the sulphur predominates, and one of an orange hue, in which the arsenic is in excess. The former is the most lasting, but it is not durable in water, and still less so in oil, although not discoloured by impure air. Compounded with white lead it is soon destroyed, nor can it be mixed with any colours into which lead enters, such as chrome yellow, the old Naples yellow, &c. The sulphur in combination with the arsenic, having less affinity for that metal than for lead, lets it go, and forms a sulphuret of lead of a dark greyish hue. Moreover, as orpiment is apt to deprive other pigments of their oxygen, and therefore to change and be changed by all pigments whose colour depends on that element—metallic pigments especially—it is probable that the orpiment after some time withdraws the oxygen from the lead; and this would be an additional cause for the darkening of the tint composed of the two colours. With sulphides or pigments containing sulphur, orpiment may be used with less danger. If employed at all, however, it had better be in a pure and unmixed state. We are far from recommending orpiment as an eligible colour, and it is highly poisonous.

Brick dust and yellow ochre are sometimes found as adulterants.

50. RAW SIENNA,

Known likewise as Raw Sienna Earth, Terra di Sienna, &c., is a ferruginous native pigment, firm in substance, of a glossy fracture, and very absorbent. It is of rather an impure yellow colour, and much used in landscape, being very serviceable both in distance and foreground. Unless proper skill is exercised in its preparation, the sienna has the objection of being somewhat pasty in working. Being little liable to change by the action of either light, time, or impure air, it may safely be employed according to its powers, in oil, water, and other modes of practice. It possesses more body and transparency than the ochres; and by burning becomes deeper, orange-russet, as well as more transparent and drying.

Raw sienna compounded with cobalt, indigo, or Prussian blue, and a very little bistre, yields good sea greens, that with indigo being the most fugitive. Alone, it is adapted for shipping, sails, baskets, decayed leaves, brooks and running streams.

51. STRONTIAN YELLOW,

To justify its name, should be a chromate of strontia, a compound very slightly soluble in water, and not more stable than the zinc chromate. The pigment, however, now sold as strontian yellow is usually formed by admixture, and contains no strontia whatever. Its absence cannot be considered a disadvantage, for the substitute possesses a durability to which the original could lay no claim. Other things being equal, we prefer an original pigment to one compounded, but a good mixture is decidedly better than a bad original. A light primrose, clear and delicate.

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The foregoing comprise those yellows more generally employed, advisedly or not, as the case may be. The following are for the most part not commercially obtainable, a remark that will apply in ensuing chapters to all numbered colours printed in italics. As a rule, these have become obsolete as pigments, or have never been introduced as such. The former could not well be omitted in a work of this kind, and the latter deserve notice as being at least suggestive. At present, many of them must be regarded as mere curiosities, being obtainable only from materials of excessive rarity. In time, however, the sources whence they are derived may possibly be found in greater abundance, and these now fancy products prove of value to the palette. The new metal indium, for instance, furnishes a bright yellow sulphide, like that of cadmium. The colour could not be affected by foul air, and might possess other advantages which would render indium yellow a desirable pigment. With regard to those compounds available for artistic use, but which have not to our knowledge been adopted, several are quite ineligible. It may be thought that they are needlessly referred to, but they are mentioned as a warning and a guide. Strange preparations have been offered as pigments, and sometimes accepted, witness turbith mineral, iodine yellow, &c. In these days of chemistry there is less chance for them, but they are continually submitted to one's notice, their merits being enlarged upon in proportion to their worthlessness. Through an exceptional ignorance they may still gain a place, and it has been deemed, therefore, not superfluous to allude to them. At the same time we do not pretend to exhaust the list, any more than we claim to note all substances possessing colour, but yet not admissible as pigments. Some there are which do not retain that colour on drying; others, whose preparation involves processes too nice, complicated, or expensive, for manufacturing purposes. There are many colours, again, which exist only on paper. We have too often found the imaginations of chemical writers far more vivid than the colours they describe. Gorgeous yellows turn out dingy drabs; dazzling scarlets dirty reds; and brilliant blues dusky slates. As respects colours, most books of science need revising.

52. Arsenic Yellow,

Called also Mineral Yellow, has improperly been classed as an orpiment, from which it differs in not being a sulphide, and in containing lead. It is prepared from arsenic fluxed with litharge, and reduced to powder. It is much like orpiment in colour, dries better, and not being affected by lead, is less liable to change in tint. The presence of the litharge, however, renders it subject to be blackened by sulphuretted hydrogen. Of course it is poisonous.

53. Bismuth Yellow,

Or chromate of bismuth, may be obtained either as a lemon or an orange yellow, sparingly soluble in water. The colour is not permanent, and turns greenish-brown even when excluded from light and air.

54. Copper Yellow,

Or chromate of copper-potassa, is of a bright yellow tint, not insoluble in water. It is discoloured both by foul gas and exposure.

55. Gelbin's Yellow,

Or chromate of lime, is a pale whitish yellow, poor in colour, partly soluble, and not at all to be depended on.

56. Indium Yellow.

Whether the new metal indium will ever be found in sufficient quantity to render it practically useful remains to be seen. The most abundant source at present known is the Freiberg blende, 100,000 parts of which only yield from twenty-five to forty parts of indium. The metal is chiefly interesting in an artistic sense on account of its sulphide, a fine bright yellow resembling cadmium, and best obtained by precipitating an acetic acid solution with sulphuretted hydrogen, or sulphide of ammonium. In the latter, the yellow dissolves on being heated, but deposits again on cooling of a rather paler tint. With one modification, what was said in a former edition of this Treatise concerning cadmium yellow may be repeated of indium yellow. "The metal from which it is prepared being hitherto scarce, it has not been employed as a pigment, and its habits are not therefore ascertained." All we can tell is, that the colour does not suffer from impure air.Indium is likewise distinguished by a straw-yellow oxide.

57. Iodine Yellow,

Or iodide of lead, is one of those compounds whose presence on the palette should never have been allowed. Exceedingly brilliant, it is also utterly fugitive, destroyed by exposure or foul gas, and useless in admixture. We may state here that, whatever its colour, no pigment containing iodine can in the slightest degree be relied upon. One of the most unstable of substances, being slowly volatile even at common temperatures, iodine is or ought to be quite inadmissible as a constituent. Combined with lead, which is in itself objectionable, it forms a yellow possessing every bad quality.

58. Iron Yellow,

Or oxalate of protoxide of iron, has very unadvisedly been recommended as a pigment. It is a bright pale yellow, but soon loses the beauty of its tint when submitted to air and light, becoming, by peroxidation, red and buffy. Even in a book the colour changes.

59. Madder Yellow.

As our (the Editor's) experience of this product is somewhat at variance with that of the author, we subjoin his original statement. "Madder yellow is a preparation from the madder-root. The best is of a bright colour, resembling Indian yellow, but more powerful and transparent, though hardly equal to it in durability of hue; metallic, terrene, and alkaline substances acting on and reddening it as they do gamboge: even alone it has by time a natural tendency to become orange and foxy. We have produced it of various hues and tints, from an opaque and ochrous yellow, to a colour the most brilliant, transparent, and deep. Upon the whole, however, after an experience of many years, we do not consider them eligible pigments."

While agreeing with Mr. Field as to the character given of these yellows, we must confess that we have never been able to obtain, nor have we ever seen, a "most brilliant" madder yellow. Colours bearing that name have come under our notice, but if their hue was pure and vivid, they have always proved to be falsely so called, the madder being conspicuous by its absence. What we have succeeded in producing, and the genuine samples we have met with, have been fawns, buffs, drabs, &c., decidedly "ochrous" yellows, and wanting in stability. It is certain that no true madder yellow, brilliant and pure, ranks as a pigment at the present day. A variety known as Cory's Yellow Madder may be briefly described as Cory's Brown Madder.

60. Massicot,

Or Masticot, is a protoxide of lead, varying from the purest and most tender straw colour to a dull orange yellow, and known as Light, Yellow, and Golden Massicot. It has in painting all the properties of white lead, from which it may be prepared by gentle calcination in an open furnace. In tint with that pigment, however, it soon loses its colour and returns to white, probably extracting some carbonic acid therefrom. If used in an unmixed state, it is permanent in oil under the same conditions as white lead, but should not be employed in water, on account of its changing even to blackness by the action of damp or impure air. It is an admirable dryer, and has much the same effect as litharge in rendering oils siccative.

Litharge is merely fused massicot. Old writers speak of litharge of silver and litharge of gold, oxides of lead, pale and reddish yellow respectively. Commercial litharge, especially that which is foreign, contains sometimes a considerable proportion of oxide of copper and iron. The principal impurity, however, is generally silica, left undissolved on treating the litharge with nitric or acetic acid. Litharge is commonly used in preparing drying oils, which contain a greater or less amount of the oxide in the form of oleate of lead. Oils made siccative by means of litharge are therefore liable to be damaged by foul gas. It is a matter of congratulation that such injury is not lasting, and that the oil, like white lead, recovers its original colour on exposure to air and light. Some drying oil which we exposed on a tile to an atmosphere of sulphuretted hydrogen until it was completely blackened, regained its former yellow hue on being submitted for a day or so to air and light. Hence, although the employment of lead as a siccative is not desirable, its effects are not so deleterious as might be imagined.

61. Patent Yellow,

Turner's Yellow, Montpellier Yellow, Mineral Yellow, Cassel Yellow, &c., is a mixture of chloride and oxide of lead, obtainable either as a pale or a deep yellow. It is a hard, ponderous, sparkling substance, of a crystalline texture and bright colour; hardly inferior, when ground, to chrome yellow. Of an excellent body, and working well in oil and water, but soon injured both by the sun's light and impure air. A variety, mentioned by MÉrimÉe, in which bismuth and antimony are also used, is of greater durability.

62. Platinum Yellow.

Our own opinion of this costly preparation is that the good qualities of the product do not justify its price. It may be obtained as a bright, rich, deep yellow, of considerable transparency; but the colour is acted upon by foul gas and exposure. Even in a book we have found it assume a dirty greyish cast, and a specimen which had been kept in a drawer, wrapped up in paper, became perfectly black in a few years. The presence of palladium interferes with the beauty of the original tint, but does not affect its stability.

63. Thallium Yellow.

The new metal thallium yields in combination with chromic acid two yellow colours, a pale and an orange. They are not absolutely insoluble in water, and the sulphide of thallium being brown, would probably be damaged by impure air. But whatever their properties as pigments may be, their habitudes as such are not yet known. The present scarcity of the metal renders the colours produced from it mere scientific curiosities.

64. Thwaites' Yellow.

Under this name chromate of cadmium was introduced some few years back. If well prepared, it is a fine soft powder of a very vivid light yellow colour. The compound is too soluble, however, to be of value, its washings even with cold water being continually tinged yellow. Hence it turns green after a time, and becomes otherwise discoloured. Like citron yellow and other chromates apt to assume a green cast, it should only be employed, if at all, when compounded for foliage tints, &c. This want of durability is to be regretted, for a good sample of cadmium chrome is marked by exceeding beauty, unsurpassed for clearness and purity by any other yellow.

65. Turbith Mineral,

Or Queen's Yellow, is a subsulphate of mercury, of a beautiful lemon yellow colour, but so liable to change by the action of light or impure air, that it cannot be used safely, and hardly deserves attention as a pigment.

66. Uranium Yellow

Can be produced of a pale or orange tint, differing in brightness and depth of colour according to the mode of preparation. It is fairly eligible as a pigment, and far superior to the many fugitive compounds which have from time to time appeared. Being very expensive, however, and not possessing the good qualities of its compeers lately introduced, uranium yellow has but little chance of being employed now.

67. Yellow Carmine

Is a rich transparent colour, somewhat resembling an ochre compounded with Indian yellow. On exposure to light, it behaves much as a mixture of those pigments would do, the rich yellowness entirely disappearing, and the sober-coloured earth being left behind.

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From several metals besides those mentioned, yellows more or less vivid and durable may be obtained—from tin, nickel, cerium, molybdenum, &c.; but we do not know that any one of them would be a really desirable addition. To justify its being brought out, a new pigment should own some special advantage, chemical or artistic, by which it may be distinguished from other colours. No purpose would be answered by crowding the palette with mere repetitions, even though they were stable. If, for instance, indium yellow were found exactly similar to that of cadmium, in colour, opacity, permanence, its presence would be quite superfluous. The mistake is often made of offering a fresh compound for a pigment when something as good or better, and cheaper may be, already exists. We remember a patient experimenter, who had produced a pink from cobalt, wondering why his colour should be so generally declined. The product was not wanting in either beauty or stability, but he forgot that the lakes of madder were far more beautiful, at least as durable, and much less expensive. We have said that we do not join in the cry of there being too many pigments, or share the opinion that there is not room for more, but we do enforce the necessity of progress. Let us have as many good colours as possible, but let the new be superior to the old, and all be distinct from each other.

As far as yellows are concerned, the palette possesses both variety and durability. Opaque or transparent, bright or subdued, deep or pale, it presents a sufficiency of permanent pigments. Most noteworthy are aureolin, the deep and 'pale' cadmiums, lemon yellow, Mars yellow, the modern Naples yellow, the ochres, orient yellow, and raw sienna. Whether used alone or in tint these are, if genuine, perfectly reliable, and comprise the list of those durable colours which may be called pigments of the first class.

Among pigments of the second class, or the semi-stable, gamboge holds the foremost place, for although not strictly durable in itself, it conduces to the permanence of other colours. Chrome yellows, citron yellow, strontian yellow, and Thwaites' yellow, also belong to this division.

As third class pigments, or the fugitive, must be ranked Mutrie yellow and other lemon cadmiums, the true gallstone, Indian yellow, the lakes, orpiment, Gelbin's yellow, massicot, patent yellow, and turbith mineral.

It must not be forgotten, however, that these three classes are subject to modification. A durable pigment may be so adulterated as to descend to the second or even the third division, while a semi-stable or fugitive colour may be replaced by a permanent or comparatively permanent substitute, as in the case of strontian yellow and gallstone. It should likewise be remembered that pigments are apt to vary in stability according to the mode of their preparation; and that, as there are different degrees of permanence, there are different degrees of fugacity.

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