Q. Your article on Mary Cassatt (March 2000) mentioned that the blue paper she used for her pastels has faded to a tan or gold hue because the dye wasnt lightfast. Could this have been caused by the papers acid content? In general, is it safe to use pastels on acidic paper or paper labeled fugitive?
Douglas A. Fales
A. The coloring materials used to make many blue, gray and green papers in the 19th century were not lightfast, and their fading over the years has left the paper colorless. But the papers fiber was often poor quality, wood-pulp-based cellulose that discolored to brown or gold as it became more acidic with age, so the discoloration of Cassatts paper is probably the result of both faded coloring materials and degradation of the cellulose fibers. In fact, this is the case with most damage to 19th-century papers.
Furthermore, a change in the pastel support results in a change in the pastel itself. This is a fragile medium thats at great risk when the support darkens and embrittles, so choose your paper carefully. Modern acidic papers and papers labeled fugitive both may dramatically change the appearance of your pastel paintings by allowing either the color to fade or the paper to darken. Very few colored papers on the market today are lightfast.
Its easy to test your papers lightfastness by placing a small sample in a window with southern exposure for a few months and a second sample in a dark drawer. Compare the two side by side after six months, and again after one year. And dont forget to test your pastels by the same method. Conservators and pastel manufacturers have recognized that pastels in the high valuesthose mixed with a lot of whiteare especially vulnerable to fading and, unfortunately, some manufacturers also use fugitive dyes in their pastels. Judging your pastels should become easier, though, because the American Society for Testing and Materials is currently testing the lightfastness of pastels in order to develop a lightfastness rating standard.
Mark Gottsegen is an associate professor of art at the University of North Carolina at Greensboro.