Describes paper materials with a pH of around 7.0. These materials are considered acid-free and are less likely to harm artwork. Paper materials with a pH below 6.5 or above 8.5 are not considered acid-free for the purposes of picture framing, and will over time (e.g. years) – break down and leach acid into parts of the artwork that it comes into contact with, creating yellowish-brown stains on the artwork. Acid-free materials are more permanent and less likely to discolour over time. The term Archival or Conservation quality more accurately describes true acid-free conservation quality matboards.