NOOOO……… NOT COLORED CHALK!
A couple days ago a person from a local arts council where I maintain a membership was viewing my art prior to hanging some in their exhibition area. She made the observation that she never thought of pastels having such bold, vibrant colors. Alas, that is what so many people believe about pastels. What a mistaken impression! Another misconception is that pastels are merely colored chalks. That may be a matter of semantics, however, their manufacturing process is similar. So, let’s tackle the differences.
I’ll take the colored chalk issue first. What is chalk? To put it in simple terms, chalk is made from finely pulverized limestone (calcium carbonate), quarried from the earth. The powdered limestone is mixed with dry, powdered pigments if colored chalk is desired instead of white chalk. Water is added to make a slurry about the consistency of clay, then extruded into long, uniform “strings” about two feet each on sheets holding five strings. The sheets are placed in an oven where the strings bake at about 188 degrees F. After the chalk strings are cured, about four days, the strings are cut into the standard chalk lengths we all are familiar with, boxed, and shipped to customers. This medium is used widely in schools, and for sidewalk drawing. It wipes away and washes away easily. Colored chalks have a low volume of pigment material, which results in pale colors.
Now, what are pastels? In simple terms again, the chief ingredients for pastels are methylcellulous, a non-greasy binder, and pure, powdered pigments. The methylcellulous is just enough to make the pastel mixture adhere into sticks so that they can be picked up and stroked on a surface without crumbling uselessly. In addition, however, there may be added clay and oils. This mixture makes a slurry the consistency of tooth paste. Like chalk, it is also extruded onto sheets of about five strings. Pastels, however, must have a little moisture, so they are air-dried rather than cured in an oven. Because the binding content in pastels is so low compared to all other art media, such as paints, and certainly colored chalks and pencils, they produce the purest color saturation with a velvety texture unlike any other medium. Thus, their colors and effects are the most vibrant and vivid of all the art media out there. The small amount of oils and binder used in pastels produce buttery smooth consistency, and help the pigments adhere to the surfaces they are applied upon. They do not work well on slick surfaces, however, so a little “tooth” on the painting surface works well.
Because their pigments are so pure, pastels are very color-fast, however, they should be protected from prolonged exposure to UV light and moisture just like any other fine work of art. Pastels won’t turn yellow, crack, or darken over time, making them the most durable of all art media if properly protected. With proper protection, pastels can last for decades and centuries. Some surviving pastel paintings and drawings from the 16th and 17th centuries have survived just as fresh and beautiful today as they were when they were created. See my blog post, “What About That Glass?” for the UV protection advantages of museum quality glass for framing pastels.