Colored earths are obtainable in red, yellow, brown, and dull green. The prehistoric artists evidently did not know the greens, but they used all the others. Colored earths are not found naturally in lumps, like natural chalks, which can be used as they are for drawing; and archeologists could not at first explain how the paleolithic artists applied their colors, for there is no trace of brush or pencil stroke in their cave paintings.
All that could be found were pieces of hollow bone, the tibias of animals, containing traces of color on the inside. This discovery gave rise to the ingenious explanation that prehistoric man had blown colored powder onto the walls of the cave through these bone tubes.
Presumably these archeologists had heard of spray painting, but it did not occur to one of them to tryout this method which they had offered with such finality.
The experiment would be entertaining: someone takes a large marrow bone, scrapes out the marrow, sprinkles colored powder into it, and blows hard into one end. After the dust cloud has settled, a few grains of powder may be seen on the wall, but no one will be able to recognize any shape or form. To be effective, spray painting requires a strong blast of air through a narrow pipe which sucks thin fluid color from a second pipe and atomizes it in a cone. The only way to produce a definite
shape with a spray it to use a stencil. Also, it would be impossible to make a satisfactory atomizer out of a marrow bone, which could function only as a very crude spray.
In the author's opinion, prehistoric man discovered and used a much simpler and more effective method: the color was ground between two stones and mixed to a dough-like paste with water and some binder - the sticky juice of spurge-like plants, milk, blood serum, or egg white - and then pressed into the hollow bones. The filled bone was put to dry in the sun or in warm ashes until a finished drawing pastel fell out. The damp mixture would not stick to the inside of the bone because the marrow would have left a lining of fat, and the evaporation of the water in the mixture would make the paste contract as it dried so that it fell easily out of the bone holder.
There is no proof that this is the method used in prehistoric times, but anyone can make pastels in this way and draw with them. The applied color can be rubbed and spread with the fingers so that no trace of the strokes remains.
Modern pastels are made in exactly the same way. Gum tragacanth is used as a light binder, and instead of the marrow bone, metal or wood moulds are used. Color paste can also be prepared on a board and then rolled into shape by hand before it dries. In the section on Painting, techniques for which it is advisable to make one's own color sticks will be suggested.
In general, pastels are more a painter's than a draftsman's material. However, if only one pastel color is used, such as red or sepia, or another discreet dark tone, the result is generally conceded to be a drawing. This, at any rate, used to be the rule. When the artist uses an additional color or two, the strict division between a drawing and a painting may become uncertain, as in some pastel works by Degas or Toulouse-Lautrec. However, painting is usually thought to begin when several colors are applied and overlap or merge.
Refill pencils are made to hold leads up to a thickness of only about one-fifth inch, and a special chalk holder or "porte-crayon" is made for charcoal and pastels, since they are so fragile. The holder makes it possible to use short ends, and it is even more comfortable with longer, unbroken chalks. Three or four springy blades protrude from a handle, and a ring passes over them to hold them close around the chalk.