Field's Chromatography / or Treatise on Colours and Pigments as Used by Artists

by George Field

A principal test of permanency in pigments is the impunity with which they bear exposure to light and air, an artistic proof of their stability the mere chemist is apt to neglect. Provided the colour remain unaffected by sulphuretted hydrogen, &c., he seldom hesitates to pronounce it safe. But a pigment may be fast in one sense and fugitive in another, believed in by the laboratory, and found wanting by the studio. It has happened before now that the same colour has been dubbed durable and the reverse, by the man of science and the man of art. The former, we take it, looks upon a pigment as a coloured substance of a certain composition, possessing maybe an acid and a base, either, or neither, or both of which, gases and other reagents may injure or destroy. The latter views a colour chiefly as part and parcel of his picture—that picture which may meet with foul exhalations, but must be exposed to light and air. And he too often thinks as little of the effects of an impure atmosphere or injudicious admixture, as the chemist considers the action of air and light.

With the exception of madder, those colours mostly affected by light and air are of organic origin, such as gallstone, Indian yellow, and the yellow dye-wood lakes; the red and purple lakes of cochineal; indigo; and sap green. To these may be added the semi-organic Prussian blue; and the inorganic yellows and orange of arsenic.

The pigments liable to injury from sulphuretted hydrogen, &c., are notably those obtained from lead and copper; and that treacherous compound of iodine and mercury, known as pure scarlet.

Many colours are apt to change from the action of white lead and other lead pigments, &c., principally those which are altered by light and air.

Many, too, cannot safely come into contact with iron, or ferruginous pigments; especially the yellows of arsenic, the lakes of cochineal, and the blues and greens of copper. With these an iron palette knife is best avoided, one of ivory or horn being used instead. The latter, indeed, is preferable in all cases, several pigments being slightly affected by iron, cadmium yellow among the number.

Numerous colours are likewise injured by lime and fire, and cannot therefore be employed in fresco, or enamel painting.

Of substances which may act deleteriously on colours, there remain the vehicles and varnishes with which they are mixed. Many of these have been blamed, and often with justice, for their injurious effects on pigments. The reputation of the most permanent colour may be ruined, if the vehicle, &c., employed with it be untrustworthy. The presence of lead, for instance, in such materials renders them liable to be blackened by foul air, and by consequence the pigments used therewith.

Time produces in many cases a mellow and harmonious change in pictures, but occasionally alterations altogether unfavourable. To ensure the former and prevent the latter, the attention of the artist in the course of his colouring should be to the employment of such pigments and colours as are prone to adapt themselves, in changing, to the intended key of his colouring, and the right effect of his picture. Thus, if he design a cool effect, ultramarine has a tendency through time to predominate and aid the natural key of blue. He will, therefore, compromise the permanence of this effect, if in such case he employ a declining or changeable blue, or if he introduce such reds and yellows as have a tendency to warmth or foxiness, by which the colouring of many pictures has been destroyed. In a glowing or warm key, the case is in some measure reversed—not wholly so, for it is observable that those pictures have best preserved their colouring and harmony in which the blue has been most lasting, by the pigment counteracting the change of colour in the vehicle, and that suffusion of dusky yellow which time is wont to bestow upon pictures even of the best complexion.

Unless introduced and guaranteed by houses of acknowledged reputation, newly discovered pigments are to be used with caution. Good colours have ever been prized with so true an estimation of their value, that to produce such, after so many ages of research is no ordinary accomplishment. But too many resplendent pigments, fruits of the fecundity of modern chemistry, have been found deficient. The yellow and orange chromates of lead, for instance, withstanding as they do the action of the sunbeam, become by time, foul air, and the influence of other pigments, inferior to the ochres. So the dazzling scarlet of iodine and mercury must yield the palm of excellence to the more sober vermilion, being a chameleon colour, subject to the most sudden and opposite changes. And the blues of cobalt, as always tending to greenness and obscurity, cannot rank beside ultramarine.

We are far from asserting, however, that all modern pigments are inferior, or that pigments should be looked upon with suspicion because they are modern. Several most valuable colours have lately claimed attention, notably the permanent transparent yellow called Aureolin. Seeing that, until its introduction, a yellow combining transparency with a perfect stability was unknown to the palette, the importance of such an addition, so long wanted and wished for, cannot be overrated. Equal in beauty and durability with the preceding, but possessing greater richness and depth, and of a semi-opacity, another yellow of the highest order merits regard, Orient Yellow, distinguished for its lustrous golden hue, resembling a bright Indian yellow. Dazzling in brilliancy, and absolute in permanency. Cadmium Red next attracts notice. This new aspirant for artistic fame is a most vivid orange-scarlet, the latter colour predominating, of intense fire, but with no approach to rankness or harshness, yielding delicate pale washes, and blending happily with white in the formation of flesh tints. With it may be coupled Cadmium Orange, a colour equally brilliant and stable, and equally without rankness or harshness, but of a true orange hue, admirably adapted for sunsets and the like. Last of all the fresh pigments of whose thorough durability there is no doubt, comes the splendid Viridian, a green nothing but fire will change, and no mixture of blue and yellow will afford. Clear, bright, and transparent as the emerald, it rivals velvet in its soft gorgeous richness. With this and Aureolin a series of beautiful foliage tints may be formed, sparkling with sunshine, as it were.