Pastel, as compared with wax, is a comparatively modern process. It was known in the seventeenth century, but it was not until the eighteenth century that it came into widespread use, though since then it has remained continuously in favour.
The essential feature of pastel is that the pigment is mixed with a small amount of medium, and moulded into sticks or cakes; and is then applied directly to the support by hand. Usually, the pigment is first mixed with a filler, usually pipe-clay or whiting. This improves the covering power of the pigment, i.e. its power to conceal the surface to which it is applied; and by mixing different amounts of pigment with the filler, a wide range of colours can be obtained, which since the filler is white, are many of them the pale soft tints called commercially ‘pastel shades’.
The binding medium used is usually gum tragacanth, a gum of which only a small part is soluble in water, but which swells to form a sticky mass with which the pigments are mixed. Many other substances may be used, however, such as skimmed milk and soapy water; while Russell, one of the leading English pastel painters, used spirits of wine, evidently relying upon resinous impurities therein to act as a binder.
The pigments used in pastel are only limited by the fact that the medium or binder encloses the particles imperfectly, and is apt itself to be fragile, so that its protective power against external impurities or interaction between pigments is not great. Thus, as Russell points out, white lead, which is very satisfactory when protected by oil, in pastel tends to turn black owing to sulphur in the atmosphere. The use of poisonous pigments (e.g. those containing lead or arsenic) is also to be avoided from the painter’s point of view, since he may breathe-in the dust which it is difficult to avoid making when using pastel.
As a material pastel is to be distinguished from the harder chalk crayons, much used by artists for drawing, in which the pigment is mixed with an oil or wax, and moulded into sticks. Confusion is apt to arise, since pastel is sometimes called crayon, especially in the eighteenth century.
The support is generally paper, though canvas is sometimes employed, and occasionally vellum. Russell notes, however, that vellum is liable to mildew in an unfavourable climate, which will change the colours. Generally, paper is pasted on to linen or fine canvas, mounted on a wooden frame or stretcher, or mounted on millboard; canvas is either mounted on a stretcher or on millboard. This mounting is desirable to give firmness.
The surface of the support is often treated to give it the necessary tooth to hold the pastel. According to Russell, Maurice Quentin de la Tour, one of the greatest exponents of pastel, used to brush over the paper with gum water, and sprinkle this with smalt, a vitreous blue pigment. This gave him both a suitable tooth and a tinted ground on which to work. Finely ground pumice stone is today a usual material for this purpose.
In using pastel, if a preliminary drawing is necessary, Russell recommends that it be made on another piece of paper, and then transferred to the surface on which the painting is to be made; the reason being that erroneous strokes of the sketching chalk, which contains grease, will prevent the pastel adhering to the surface. The pastel painting can be built up in a succession of touches which are left undisturbed.
More usually, however, especially in the eighteenth century, the design is laid in with a few colours, which are then to a certain extent fused by rubbing with the fingers or with a stump. Russell mentions the use of carmine, white, and black for this ‘dead colouring’. The final touches are then put on direct and left untouched as may be seen in a detail from a pastel by Mary Cassatt (Pl. VII b).
Variations in the proportions in which rubbing and direct touches are used can give a wide range of effect; and are found not only from artist to artist, but in the work of the same artist. De la Tour, for example, used rubbing extensively, while his contemporary, Perronneau, gave more prominence to the unfused touch. Russell points out one peculiarity of pastel. Since it is difficult to get very dark pastel colours, owing to the white filler with which the pigment is mixed, the painter must make his picture as rich and dark as possible at the beginning; and if the light tints become predominant, they will continually work up through darker colours.
Applied direct, pastel yields a delicacy and luminosity at least equal to that obtainable by any other process. The pigments, held very lightly in the medium, can reflect the maximum of light, and on occasion can literally sparkle. Moreover, if the pigments are properly chosen, from the point of view of permanence, the whole painting lasts well, since the filler with which the pigments are mixed is inert, while the medium is not unduly liable to change or decay, and so involve such troubles as cracking.
On the other hand, the range from dark to light in pastel, owing to the mixture of white with the colours, is less than in some other processes, notably oil. Also, pastel is not easy to handle so that its full beauty is realized. If rubbed too much, the colour may become dull and lifeless. Moreover, it is difficult to make corrections or to work over the surface without the paint becoming muddy. Another problem for the user of pastel is to ensure that the pigments he uses are reasonably permanent. Pastels supplied commercially are sometimes only chalk stained with dyes of which the colour will soon change or disappear.
Consequently, it is often recommended that the artist make his own pastels. Pastel’s worst defect, however, is its fragility. It is very loosely held on the support or ground, especially when it is used lightly and directly, in the most effective way to realize its qualities. A painting in pastel must always be kept under glass, to avoid the risk of an incautious touch, and a sudden knock or continuous jarring, such as that due to traffic, will almost certainly shake the paint from the surface.
This fragility has been the cause of many experiments with fixatives for pastels, such as a transparent resin (e.g. shellac) dissolved in a volatile liquid, which is sprayed on the surface. This surrounds the particles of pigment and filler, and helps to bind them together and secure them to the ground, and so becomes part of the medium. But, inevitably, it also tends to saturate the particles, and to make them more transparent, so reducing the brilliancy of the colour.
Degas, who used pastel superbly, is reported by Vollard never to have used commercial fixatives, since they gave a shine to the surface, and changed the colours. A fixative was particularly necessary for Degas. He is said to have worked over his pastels a great deal, fixing each layer to secure good adhesion among the different layers; and then to have completed the work with touches of pure pastel. Probably from these last touches comes the powder colour often found at the bottom of the frame of a Degas pastel.
Pastel is sometimes effectively combined with other processes, to give sparkle and liveliness to the final touches. Degas, again, sometimes used it in combination with much thinned oil paint, which dried with a mat surface. More often, it has been used in combination with water-colour, which in most of its uses does not affect the tooth of the surface to which it is applied.
Another attempt to combine the advantages of pastel and to avoid its defects was that of J. F. Raffaelli, the Impressionist painter. He had pigments made up into sticks with a softer wax than that used for crayons, as being stronger than the binder of ordinary pastel. These sticks could then be used like pastel, giving a similar effect. But the result could be varnished, to give a shiny surface; or some wax solvent such as turpentine could be lightly applied, slightly to fuse the colours; or again, the colours could be applied to a painting begun in oil, and the whole varnished. In fact, the process never attained any popularity, but references to it are sometimes made, and it is therefore mentioned here.
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