Definition of Acid free paper

Acid-free paper is paper that has a neutral or basic pH (7 or slightly greater). It addresses the problem of preserving documents for long periods. Paper made from wood-based pulp that has not had its lignin removed goes yellow and deteriorates over time. When exposed to light and/or heat, the molecules in the wood-pulp (or acidic) paper will break down even faster. It was only in the 1930s that the effects of wood-pulp paper became known, when William Barrow (a librarian) published a report about the deterioration of acidic paper in our libraries. For fear of the gradual disintegration of written materials, measures have been taken to improve the quality of paper.