Artists of today have the advantage of a more extended palette than the old painters had. Some, however, may say that this is a doubtful advantage, but it cannot be denied that in addition to our still possessing the best of the old colours, there are quite a number of even more permanent ones, notably of green and yellow pigments, which chemists have added to the modern artist’s colour box. Also, the more perfect grinding of them by modern machinery methods render them finer in texture and even superior in some ways to the older pigments. A few of the old colours mentioned by ancient and mediaeval writers are now unknown to us, or at least cannot be recognized under the names that were formerly given to them, as half-a-dozen terms of different etymology were sometimes applied to the same pigment, which has tended to obscure or confuse their identity.
MODERN YELLOW PIGMENTS.The most important of the modern yellow pigments is Cadmium, which is prepared in two or three shades, from a pale yellow to an orange or a red colour, and is perhaps the most brilliant yellow known. The cadmium yellows are sulphides of cadmium, and if well prepared are very tenacious in the keeping of their own sulphide, but if badly made they will likely contain some free sulphur, and if used with flake white or any colour which has lead in its composition, such as chrome yellow, the free sulphur of the cadmium uniting with the lead of the other pigment will form a black sulphide of lead, which will ultimately cause the yellow mixture to become greenish, as black and any bright yellow when mixed will make a green in a visual sense, though not in a chemical one. The best prepared form of cadmium yellow, and particularly those of the medium and darker varieties, may be safely used with flake white, and may be used in fresco and other mediums, but the paler cadmium is more fugitive, and not reliable. Cadmium yellow destroys all copper greens by turning them to a coppery brown, and more particularly the brightest kinds, such as emerald green. Doubtful forms of cadmium can be used with safety in mixture with zinc, or Chinese, white.
LEMON YELLOW is known also as Baryta yellow, and Yellow Ultramarine. It is a chromate of barium, or may be a chromate of strontium, and may be considered as a permanent colour under most conditions. It is not safe, however, to use it in mixtures with colours which are obtained from the oxides of iron, such as the ochres and siennas, as it dulls them, and ultimately such mixtures disintegrate and fall off the surface of the fresco, water colour, or wax paintings. Lemon yellow, however, can be safely used in mixture with lead or any other pigments than the oxides of iron.
Permanent yellow is a mixture of lemon yellow and zinc white, or, it may be made from a chromate of zinc, and zinc white. It is also a permanent pigment, though rather pale to be of much use as a yellow. Primrose yellow is another of these classes of pigments. It is a pale chromate of zinc, and is also known under the name of zinc yellow. These pale yellows are well adapted for use in painting the lighter tones of green draperies or of other darker greens such as foliage, etc., when such greens as the oxides of chromium are used, as all these pigments, used either alone or in mixtures, are perfectly permanent.
CHROME YELLOWS. These yellows are all chromates of lead with the addition of sulphates of lead and lime. They are dense and brilliant pigments, and are made in different shades, such as pale, or ” lemon chrome,” deep chrome, and orange chrome. The orange variety is produced by boiling the lemon chrome with caustic lime, and as the temperature rises the colour deepens to orange or even to red. Though chrome yellows are useful in common painting work they should not be used as artists’ pigments, as they are all subject to the same injurious action of sulphuretted hydrogen gas, contained in foul air, like all lead pigments. They also tend to become green, by the process of reduction, when mixed with organic pigments, or with cadmium yellows. Orange chrome is more permanent than the yellower varieties.
It may be worthy of mention that chrome yellow was a favourite pigment with Holman Hunt, who declared that it had kept its colour in his pictures for many years. He used it in sunset skies, and notably in his picture of the ” Scapegoat.”
INDIAN YELLOW is a uriophosphate of lime, and is a transparent dark yellow of not much body. It is claimed by some to be permanent in fresco, as the lime of the plaster does not affect it. This may be true if it is used so alone, but if it is used in any medium, or mixed with any pigments that contain or impart oxygen, its yellow colour will be darkened beyond recognition.
GREENS.The most permanent modern green pigments are those known as the Oxide of Chromium, a dense and opaque colour of great body, and the Emerald, or Transparent Oxide of Chromium. The former is a combination of oxygen and chromium, and a variety of this kind is known as French veronese green. The transparent variety is the hydrated oxide ; a deep bluish green, rich in colour but not so brilliant as the pigment commonly known as Emerald green. This hydrated oxide is also known as viridian. Both of these important chrome greens are perfectly reliable in any medium, and do not injure any other colours when mixed with them. The only exception to this is, that the hydrated oxide cannot be used in enamel painting on account of its having some water in its composition. Another form of this pigment is known as ” Vert de Guignet,” which is said to have some borax in its composition.
There are also other greens which go under the name of chrome greens, but these are generally composed of mixtures of chromate of lead and Prussian blue, and are not at all reliable as artists’ colours.
EMERALD GREEN, the brightest of all greens, Brunswick green, and Scheeles green are all similar in composition, and are prepared from copper, acetic acid, and arsenic. They are all injurious to other colours in mixtures, are altered in colour by the action of the air, and are highly poisonous. Emerald green is the most reliable of these copper greens, when used by itself, or in mixture with zinc white, and is fairly permanent when used in a varnish medium.
BLUES. Prussian blue is a comparatively modern pigment, being discovered in the eighteenth century. It is a dark and intense blue of great body, or staining powers, and consists of a chemical composition, known as a ” ferro-cyanide of iron.” It is a cyanogen blue, one of the compounds of iron and cyanogen. It is made by adding a solution of the ferro-cyanide of potassium, the yellow prussiate of potash, to a solution of a persalt or per-oxide of iron such as the sulphate of irongreen copperasor to a nitrate or a muriate of iron. Other blues, similar in composition, are known as Paris blue, Chinese blue, Antwerp blue, etc., and are all ferro-cyanides of iron. All these pigments dry well, and when used alone, or in mixtures with zinc white, or with sienna earths they are fairly permanent, but lime and all alkalis destroy ferro-cyanide blues. They should not be used with linseed oil, or they soon become green, but in a varnish and turpentine medium they keep their colour fairly well.
CERULEAN blue is an artificial colour resembling a mixture of cobalt blue, zinc white, and a little yellow, which gives it the slight tinge of green. The commoner kind of cerulean is a mixture of zinc white, ultramarine, and Naples yellow, but the best modern variety is a stannate of cobalt. The ancient Egyptian blue resembling cerulean, was obtained from a carbonate of copper. The modern pigment has a dense and opaque body, it is very permanent, and can be used in fresco.
New blue and Permanent blue are simply modern varieties of artificial ultramarine, darker and lighter, respectively, to the latter, and both inclining towards the hue of cobalt.
REDS.With the exception of the reds obtained from alizarin, the modern product of coal tar, there are hardly any reds, worthy of the artist’s notice to-day, that were not known to the old painters. The alizarin reds are modern imitations of the crimson and madder lakes. The colouring matter of alizarin is identical with the red colour product of the madder plant, the Rubia tinctorum. It is therefore much more permanent than the red which is obtained from the cochineal insects, used in the preparation of crimson lake. Alizarin crimson is not quite so pure in colour as madder lake, but it is quite as permanent as the latter, and is subject to the same conditions as madder lakes when used as an artist’s pigment.
BROWNS.Brown madder is a composite colour made as a mixture of madder lake and burnt sienna, or an iron oxide, or, it may be a mixture madder lake and black. It is almost permanent, but in time generally loses some of its brilliancy. Sepia is a transparent brown derived from the cuttlefish, but more often made from walnuts.
Prussian brown is a good and permanent colour made by calcining Prussian blue. It is a very transparent iron brown of a yellowish hue. An-other form of Prussian brown is prepared from a solution of blue copperas added to a solution of yellow prussiate of potash. This is a copper brown.
We have now noticed and described the more important and useful pigments that are manufactured at the present day, omitting many others that are not worthy of the artist’s attention, on account of their doubtful qualities or unreliability, and others which are merely mixtures of certain colours, as the case is with some greens, oranges, purples, browns, and greys. As regards some pigments that are not noticed in the above description, but are in common use to-day, it may be pointed out that they have been already described in the former chapter which deals with the colours used by the old painters.