In even the most beautifully framed art, there may be an unseen threat ready to destroy. Naturally occurring acid in paper and framing materials can cause yellowing, deterioration and ruin not only the frame and mat, but the art as well. Although it may look polished in the beginning, artwork that yellows and turns brittle won’t be worth displaying for long.

The art to showing art goes beyond composition and spacing; the materials used to frame art are equally important to maintaining beauty over time. Selecting framing materials that are acid-free will make a great difference in the longevity of framed artwork.

Acid-free vs. Non-acid-free

To understand acid-free and non-acid-free paper and framing materials, we need a quick review of chemistry. pH (acid) is measured on a scale of zero to 14. pH neutral is seven; anything below seven is acidic and anything above is alkaline (non-acidic). Acid-free paper has a pH rating above seven.

The main source of paper and matting-discoloring acid is lignin. Lignin is a chemical compound found in the pulp of paper that produces acid as it deteriorates. It occurs naturally in trees and other plants and holds wood fiber together, making it is an obvious component of plant-based paper.

While most paper is made from wood pulp, true acid-free paper is made from cloth or rags. This removes the threat of lignin. Completely acid-free paper is known as rag board or museum rag board. Other paper materials used in art and framing are called wood-pulp paper or pulp paperboard. Paper can be acid-free and still contain lignin, however. Most quality acid-free papers are manufactured to have a minimal amount of lignin and neutralized to prevent fading and yellowing. In this manner, wood pulp based materials can be made essentially acid-free.

In these products, acid is neutralized during the manufacturing process and lignin is eliminated in two ways:

1.Removing lignin from pulp: Lignin is chemically separated from wood fibers when wood pulp is created for the production of paper.

2.Buffering: Alkaline, or base substances, are added to neutralize acids in the pulp when paper is made.

Damage Done by Non-Acid-Free Materials

If you’ve ever removed the frame off of an old black and white photograph and discover discoloration under the frame, this if the result of acidic paper over time. When exposed to the elements, the acid in paper, matting and frame backings can change the chemical composition of the artwork, affecting color and image clarity.

Another form of damage is chemical burning. When wood pulp, which is essentially sulfur, combines with water in the atmosphere, you get sulfurous acid. All non-acid-free paper lets off a microscopic fuming of sulfurous acid, which causes paper to become dry, brittle and brown.