Working well is a quality which depends principally upon fineness of texture, and what is called body in colours; yet every pigment has its peculiarities in respect to working both in water and oil, and these must become matter of every artist's special experience. Some of the best pigments are most difficult of management, while some ineligible colours are rich in body and free in working. Accidental circumstances, however, may influence all pigments in these respects, according to the painter's particular mode of operation, and his vehicle; upon the affinities of colours with which depend their general faculties of working—such as keeping their place, crispness or setting up, and drying well. These latter, with other properties and accidents of pigments, will be particularly considered in treating of their individual characters; but it may be remarked that crispness or setting up, as well as keeping their place and form in which they are applied, are contrary to the nature of many pigments, and depend in painting with them upon a gelatinous mixture of their vehicle. For example, mastic and other resinous varnishes impart this texture to oils which have been rendered drying by the acetate, or sugar of lead:—simple water, also albumen, and animal jelly made of glue and isinglass, give the same quality to oils and colours; and bees-wax has a similar effect in pure oils. Whitelac varnish, and other spirit varnishes, rubbed into the colours on the palette likewise enable them to keep their place very effectually in most instances. This is important, because glazing cannot be performed except with a vehicle which keeps its place, or with pigments which lend this property to the vehicle, as some lakes and transparent colours do.
Fineness of texture is produced by extreme grinding and levigation. Pigments ground in water in the state of a thick paste, are miscible in oil and dry therein firmly; and in case of utility or necessity, any water-colour in cake, being rubbed off thick in water may be diffused in oil, the gum acting as a medium of union between the two. Thus, pigments which cannot otherwise be employed in oil, or varnish, may be forced into the service and add to the resources of the oil-painter, care being taken to use the palette-knife, if of steel, with caution.
Desiccation or drying. The well-known additions of the acetate, or sugar of lead, litharge, and sulphate of zinc, either mechanically ground, or in solution, for light colours; and japanner's gold size, or oils boiled upon litharge, for lakes; or, in some cases, manganese and verdigris for dark colours, are resorted to when the pigments or vehicles are not sufficiently good dryers alone. It would be well if lead and copper could be banished from the list of siccatives altogether: assuredly, no artist with any regard for the permanent texture of his work should employ them except in extreme cases, and in the smallest possible quantity. The best of pigments may be ruined by their injudicious use, and obtain a character for fugacity which they in no way deserve. It requires attention that an excess of dryer renders oil saponaceous, is inimical to drying, and is otherwise injurious. Some colours dry badly from not being sufficiently edulcorated or washed. Sulphate of zinc, as a siccative, is less powerful than acetate of lead, but is far preferable in a chemical sense. It is supposed erroneously to set the colours running; which is not positively the case, though it will not retain those disposed to move, because it wants the property the acetate of lead possesses, of gelatinizing the mixture of oil and varnish. These two dryers should not be employed together, since they counteract and decompose each other, forming two new substances—acetate of zinc, which is a bad siccative, and sulphate of lead, which is insoluble and opaque. The inexperienced ought here to be guarded against the highly improper practice of some artists, who strew their pictures while wet with acetate of lead, or use that substance in some other mode, without grinding or solution; which, though it may promote present drying, will ultimately effloresce on the surface of the work, throw off the colour in sandy spots, and expose the paintings to peculiar risk from the damaging influence of impure air.
It is not always that ill drying is to be attributed to the pigments or vehicles, the states of the weather and atmosphere have great influence thereon. The direct rays of the sun are powerfully active in rendering oils and colours siccative, and were probably resorted to before dryers were—not always wisely—added to oils, particularly in the warm climate of Italy. The ground may also advance or retard drying, because some pigments united by mixing or glazing, become either more or less siccative by their conjunction. Many other accidental circumstances may likewise affect drying; and among these none is to be more guarded against by the artist than the presence of soap and alkali, too often left in the washing of his brushes, and which, besides other bad results, decompose and are decomposed by acetate of lead and most siccatives. In such cases desiccation is retarded, streaks and patches are formed on the painting, and the odium of ill drying falls upon some unlucky pigment. To free brushes from this disadvantage, they should be cleansed with linseed oil and turpentine. Dryers should be added to colours only at the time of using them, because they exercise their drying property while chemically combining with the oils employed, during which the latter become thick or fatten. Too much of the siccative will, as before noticed, often retard drying.
The various affinities of pigments occasion each to have its more or less appropriate dryer; and it would be a matter of useful experience if the habits of every colour in this respect were ascertained. It is probable that siccatives of less power generally than the compounds of lead and copper might come into use in particular cases, such as the oxides of manganese, to which umber and the Cappagh browns owe their drying quality.
To other good attributes of pigments, it would be well if we could in all cases add the property of being innoxious. As this, however, cannot be, and colours are by no means to be sacrificed on that account, cleanliness and avoiding the habit of putting the brush unnecessarily to the mouth, so common in water-painting, are sufficient guards against any possibly pernicious effects from the use of any pigment. No colour which is not imbibed by the stomach will in the slightest degree injure the health of the artist.