is for Acid-Free in the A to Z of Tools for Legacy
When considering the preservation of items for legacy purposes the composition of the individual item and the environment in which the item is placed impact the use, display, and storage of of the item.
Chemistry of Paper
Chemical composition of a substance falls along a range of acidic and base reactivity. Acids accept electrons from other materials into their chemical structure. Bases give electrons to other materials. These states are measured by pH which is the potential of hydrogen. Without technical explanation, you can grasp the essence of the 14 point scale that describes the pH of a substance. A measure of 0 to just under 7 is considered acidic while a measure of just over 7 through 14 is considered alkaline or basic.
Neither end of the 14 point scale is desirable for preservation purposes. For example, battery acid is less than 1 on the scale and drain cleaner is around 14. 7 is considered neutral and is the pH of water.
For preservation purposes 7, a neutral pH, is good, usually. But just as important is a stable environment.
For archival or preservation purposes, the chemical structure of an item should remain stable. Each type of material has a different chemical composition and that impacts optimal storage conditions.
The term “acid-free” typically describes paper that is used for archival or conservation purposes. This means it has a pH of 7 or higher.
Something could be “acid free” with a very high pH that would not be stable.
Structure of Paper
“Lignin-free” is also used to describe archival paper. Lignin are fibers in wood that hold the cellulose of the tree together. Lignin are composed of short fibers that release acids and decompose rapidly. Long-fibered papers, made from cotton and flax plants, are preferred for archival purposes as they do not contain lignin and have a more stable, much longer, shelf life.
Archival quality papers tend to be pH 7 to 9. This slight alkalinity helps counter the migration of acids as materials degrade over time. Many archival papers have a buffering agent added to pulp in manufacture to increase alkalinity as all papers decrease in pH over time.
Recommended Resources
The linked download below takes you PDF is in the public domain and is highly recommended as an introduction to conservation. It is written for government conservators is readable and useful, and only 4 pages long!
National Park Service Conserve O Gram 4.9
If you are in the market to shop for acid-free storage containers, envelopes, and boxes, check out the Container Store! This is a non-compensated plug for a very mainstream brick and mortar store that understands storage and preservation.
Online Archival Supply Companies
Nancy, the editor and publisher of WLP, has used products from both of these companies during her time working in libraries and museums, so she knows these suppliers provide good quality archival products. She has received no compensation for mentioning these company brands. Many other companies also provide archival products, just be sure to check the acid and lignin composition of all items before you order or purchase.
Legacy Tools
April 2016 A to Z Challenge
Letter A Archival Needs Tools for Legacy projects