pastel chalkWhat Makes Up a Pastel?

The basic constituents of pastel are a pigment, a filler (a white mineral which serves to give opacity and body), and a binder (a weak adhesive) that loosely holds the two powdery substances together so that they may be formed into a crayon for use. In the eighteenth century, the ideal crayon was to be sufficiently firm so it could be grasped between the fingers without breaking, yet powdery and soft enough to crumble when stroked across a support. A relatively small range of pigments (mostly the same as those used for oil painting) was used in forming an innumerable array of colors, a feature of the medium still characteristic of today’s pastel box. These pigments were combined to produce the desired hue, with proportional amounts of filler added to produce the tints. This multitude of hues allowed pastelists to work in gradations of tone rather than in color mixtures so as to produce the greatest brilliance.

Selected steps in the complicated process of making pastels

The process of fabricating pastels in the eighteenth century was complex. Many steps had to be carried out by hand and were varied according to the composition of the color, starting with the preparation of the pigment by grinding and washing. Because pigments have distinctive properties (such as cohesiveness, softness, brittleness), each had to be coordinated with a particular filler (selected from a range of materials, such as chalk, tobacco pipe clay, gypsum, and alabaster) and a suitable binder (among them, gum tragacanth, oatmeal whey, or skim milk) to produce crayons of satisfactory texture. After the ingredients were mixed together the paste was divided and rolled into crayons, cut to length, and carefully dried by air or with heat to avoid imperfections and cracks.

A Distinctive Brilliance

Pastel was praised in the eighteenth century because of the lifelike quality, or "bloom," it conferred upon its subjects. This distinctive appearance results from the physical characteristics of the medium and the way in which it reflects light. As all powders, pastel reflects light from the facets of its finely divided particles and the air spaces in between them, an effect evoking a sense of white light. In pastel this powder is composed of numerous particles of pigment and filler. Because there is only a minute amount of binder, and the powder is opaque, light does not penetrate through pastel (as it does through a varnished oil painting) but is diffusely scattered, or reflected, from the surface. This physical phenomenon accounts for its velvety, matte quality. Additionally, the absence of a varnish, which inevitably alters in color over time, accounts for the characteristic brilliance and purity of tone of pastels. This visual property was especially prized by the eighteenth-century connoisseur and consumer who similarly took delight in the bright, scintillating surfaces of contemporary interior décor, as evidenced by the profusion of mirrors, ormolu mounts and ornaments, and gilt frames popular at the time.

Pastel’s characteristic light can be impaired when a fixative is applied to a composition. Because the surface of a pastel is easily rubbed and damaged, many recipes for protective substances were devised in the eighteenth century, some even claiming to provide a means of enabling these works to be cleaned or varnished. There was, nonetheless, great debate as to their efficacy, as it was recognized that applying a resin to the surface of a pastel would darken the colors and cause them to yellow. Instead, to secure the powder to the support, artists depended upon using slightly roughened paper and careful building of the layers of color.