“Most paper has 2%–10% ceramic as a so called filler material; some papers have even more. The ceramic is actually a very important active ingredient providing paper with opacity and whiteness, while controlling the flow of ink in writing and printing. Without the ceramic, ink would be absorbed by and smear into the paper. The ceramic also can provide color. Ceramic has been used for many centuries as an important paper additive, with china clays, such as kaolin, having very long histories as the applied a material.”

—Victor Greenhut, from Ceramics for Paper in Wachtman, ed. Ceramic Innovations in the 20th Century. As quoted in Clay: The History and Evolution of Humankind’s Relationship with Earth’s Most Primal Element, by Suzanne Stauback, 2005.