Pastels are made by blending dry powdered pigments with a nongreasy liquid binding medium such as gum arabic.

The resultant paste is usually rolled into a stick and then dried.

A wide spectrum of pastel colors is possible, and by the eighteenth century, some artists endeavored to imitate the power and richness of oil painting through a coloristic and painterly style of draftsmanship, so that many of the finest pastels of the period are known as "pastel paintings."

Pastels were invented at the end of the fifteenth century in northern Italy, and it is thought that Leonardo da Vinci was the first artist to use them, although none of his pastel drawings are known today.

(look for:
Federico Barocci, Study for the Head of Christ, 1986.535
Jean-Baptiste-Siméon Chardin, Portrait of the Painter
Jean-Jacques Bachelieu, 1939.89
Hilaire-Germain-Edgar Degas, Two Dancers Entering the Stage, 1943.812
Odilon Redon, Head of a Young Woman, 1943.905).

(from artmuseums.harvard.edu/sargentatharvard/drawingglossary.html)