Field's Chromatography Part 5

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 gla.s.s. 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 quant.i.ty 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 Minerale_, _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 coa.r.s.e 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 minerale.

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 subst.i.tute, 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 princ.i.p.ally 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 s.h.i.+nes 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 varnis.h.i.+ng. 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 b.a.l.l.s 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 p.r.o.nounced 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 quant.i.ty 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 princ.i.p.al 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 subst.i.tute 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,