Archival Terms Dictionary

All the terms related to safe photo and keepsake storage can be confusing... acid-free, archival, lignin-free and more.

Still, it's critical to know what these terms mean, so you can protect your mementos and ensure their enjoyment by future generations. Exposures wants to help you make sure your memories are safe, so we've created this easy reference to help you sort out what's what.

Acid-free paper: Acid can cause paper and photos to disintegrate. Acid-free paper has had the acid removed (buffered), so it has a pH level higher than 7.0. This makes the paper more stable, so it doesn't break down or discolor over time. Acid-free paper is safe for preserving photos and other materials for long periods of time. Note that not all acid-free papers are archival quality.

Acid migration: The shift of acidity from one source to another through physical contact or acidic vapors. For example, a photo that shares the same album page as a newspaper clipping is not safe, even if they are not touching, because of possible acid migration from the newspaper.

Archival quality: Archival quality paper has a pH level between 7.0 and 8.5, so there is no chemical interaction between the paper and objects touching it. The paper will last for a very long time without breaking down or discoloring. In fact, archival products meet the standards used by curators and librarians for storing old and rare items. While all archival quality papers are acid-free, not all acid-free papers are archival quality.

Buffered paper: Paper to which calcium carbonate (colorless or white alkaline chemical) has been added. Buffering neutralizes acids that could develop over time due to aging or adverse storage conditions.

De-acidification: A treatment that neutralizes acids in paper by applying a mild alkaline solution. It does not reverse damage caused by acids before the treatment.

Lignin: A naturally-occurring bonding element that holds wood fibers together. Lignin breaks down over time, becoming yellow and brittle. (Think of an aging newspaper.) Lignin is acidic and contributes to the deterioration of photographs and paper. When it is removed, the aging process slows significantly. Most paper other than newsprint is lignin-free.

pH scale: A measure of the acidity or alkalinity of a solution. Solutions with a pH less than 7.0 are considered acidic, while those with a pH greater than 7.0 are considered basic, or alkaline.

pH-neutral: A pH level of 7.0, meaning the paper or substance contains nether acid nor alkaline.

Photo-safe: Usually, photo-safe is equivalent to “acid-free,” but don't take any chances. Unless an item also says it's acid-free or archival quality, check with the producer to be sure, because photo-safe isn't a regulated term.

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