Acid-free

A vague term, referring to a material with a pH of 7 or higher. Sometimes used incorrectly as a synonym for alkaline or buffered material. Some acidic materials are chemically neutralized with the addition of alkaline products; other materials are processed to remove the acid-producing elements. (Acid-free materials may become acidic over time due to residual chlorine from bleaching, aluminum sulfate from sizing or atmospheric pollutants.)