Pastel must never be confused with colored chalk. Chalk is a limestone substance impregnated with dyes. Pastel is pure pigment, the same pigment used in all art media. It is the most permanent of all when applied to conservation ground and properly framed.
Pastel does not refer to "pale colors". The infinate variety of colors range from soft and subtle to strong and brillant. The pure, powdered pigment is ground into a paste with a binder and then rolled into sticks.
The medium is favored by many artists because it allows the artist a very spontaneous approach. There is no drying time and no allowances have to be made for a change in color due to drying. A particle of pastel pigment seen under a microscope looks like a diamond with many facets. Pastel paintings reflect light like a prism and no other medium has the power of color or stabililty as paste. It does not oxidize and therefore will not darken, fade, yellow, crack or blister with the passage of time.
Historically, pastel can be traced back to the 16th century. Its invention is attributed to the German chemist, Johann Thiele. Today, pastel paintings enjoy the stature of oil and watercolor as a major fine art medium.