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What does "Acid-Free" Mean?

By Carol Francois
Updated May 16, 2024
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Acid-free refers to paper and paper products with a pH value of 7 or a bit higher. pH is a standard, scientific scale from 0 to 14 used to measure the level of acid in a substance. Values between 0 and 7 are considered acidic and values higher than 7 are basic.

Paper is made using a wood-based pulp that naturally contains lignin. This chemical causes paper to yellow and deteriorate over time. When paper that is exposed to heat or light, the lignin in the paper causes the molecules to break down at a faster rate. William Barrow, who published a report on the deterioration of acidic paper, first documented the significance of this process in the 1930s. As a librarian, he was deeply concerned that entire collections of valuable written materials would be lost.

As a result of his efforts, and widespread recognition of the importance of printed materials, acid-free paper is now the industry standard. Acid-free pamphlet boxes and other specialty products are available to libraries and museums to help preserve documents that were created on paper with a high acid content. In addition to these steps, the paper surface can be treated to minimize the deterioration over time. Paper material that can accept this chemical treatment must meet a certain standard of quality. Very old paper is usually best preserved by placing it is a case away from light, heat and people.

In the paper making process, acid-free paper is treated with calcium or magnesium bicarbonate. These chemicals neutralize the natural acids in the wood pulp. The chemical mixture is absorbed by the pulp and helps to stop new acid from forming. Once treated, this paper has an alkaline reserve of two percent or greater. The paper materials made with this process will be preserved for at least 100 years.

The shift to acid-free paper has an additional environmental benefit. This process uses chalk instead of clay as filler in the pulp. The changes in materials has resulted in fewer corrosive chemicals, both in the factory and in the wastewater. Creating paper requires a significant amount of water, and the acid-free process allows the same water to be treated and reused.

Specially designed archival paper that is 100% acid-free is often used for legally significant or historical documents. This type of paper has a longer life span than the 100 years provided by acid free paper. Typically made of cotton or other fabric material, this paper is more expensive, thicker and is sold through archival supply stores.

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Discussion Comments
By MrPolitic99 — On Oct 20, 2010

Besides the obvious advantage that acid-free paper products brings to the photographic industry and the way that they use chemicals that are susceptible to damage from acid full products, there is also other advantages to using acid-free products.

The mere fact that we don't want to come into exposure with acid products as human beings means that we need to be careful about using acid products in general. If acid products are harmful to our photographs in our film, delay probably harmful to us we should avoid contact with with our skin and other sensitive areas.

I think anytime we have the opportunity to use products that do not have extra chemicals in them we should do so. While sometimes this may be costly it's worth our health to take that extra step and extra precaution.

By youbiKan — On Oct 20, 2010

As a photographer, I always make sure that the products I use around my photographic prints and my film is acid-free. This ensures that I did not have damage to my photographs because of improperly balanced chemicals inside of the papers I enclose them with.

Whenever I mounted photographs onto if card stock paper or panel board, I always make sure to cc if I am using is acid-free as well. By using acid-free products you will ensure that your photographs are not damaged. It is heartbreaking to me when I see people come in to the photo lab that I work at with old photographs that have been damaged from acid adhesives and papers.

We store such precious memories and photographs and on film, that we cannot take the chance of ruining the photographs and images that we love. Be sure to use acid-free products at all times when doing with anything related to the photographic industry and its products.

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