by Laura Stirton Aust

As paper ages it often becomes yellowed or grayed.  The paper may become brittle and easily break or tear.  Some works of art on paper somehow look dingy but are in pristine condition.  Even a paper which has been carefully stored in the best of conditions usually appears less bright than a freshly made sheet of paper.  This color change is often caused by acid.  The acid may be from non-archival framing and storage materials.  Or the acid may be from chemicals used in the manufacturing the sheet. 

Acidic materials are often used to make paper.  Acidic wood pulp is the most common paper fiber.  But no matter what fibers are used to make a paper, chemicals are added to whiten or brighten and sizing is applied to make the paper less absorbent to water, inks and other art materials.  Some of these chemicals break down with time and produce acid.  Though it is well known that acid deteriorates paper, the technology to manufacture paper with less acid-producing chemicals has not been around for many years.  It is also more expensive.  Therefore, paper manufacturers charge a premium for "acid-free" materials and few machine-made papers made after 1880 and before 1980 are truly acid-free. 

Since we know acid breaks down paper fibers and causes discoloration, why not spray something on the paper to neutralize the acid?  In fact, there are such products on the market.  They were developed for libraries with shelves full of crumbling books.  They are used today for books and ephemera such as newspapers, old letters or documents, those objects prized more for content than physical appearance.  It is called deacidification spray or solution.  It contains some form of either magnesium or calcium and may be purchased at archival supply stores.  But, before considering any work of art as a candidate for deacidification there are cautions. 

  1. Deacidification chemicals often destroy paper sizing.

  2. Deacidification may give paper a pink or green cast.

  3. Deacidification may leave paper gritty or coarse.

  4. Deacidification may change paper surface texture.

  5. Deacidification may cause shifts in ink colors, bleaching or darkening them.

  6. The longevity of deacidification is unknown. (What will the paper look like in 25 years?)

With these possible negative consequences in mind I choose only to use deacidification as a last resort for artwork.  Pieces which may not be bathed and have become dangerously brittle may benefit from deacidification.  Also, objects on very thick acidic cardboard may be sprayed from behind in hopes that deacidification will slow down the acid penetrating the artwork. 

The discoloration of an acidic sheet of paper is a result of damaged paper fibers.  Bleaching to remove this discoloration is counterproductive because bleaching can be extremely damaging to paper fibers.  Deacidification on the other hand, is meant to help protect the fibers and in some instances may reduce discoloration.  But, a collector should not attempt deacidification of artwork.  When deacidification is the correct course of action for a discolored work on paper the job should be done by a professional conservator.

If deacidification and bleaching are not the answer to a discolored paper support, what is?  When possible bathing is employed to reduce the acid deterioration.  Conservators use distilled or deionized water which may be treated with chemicals to neutralize and rinse acid out of the paper.  This usually removes some of the discoloration and may prevent accelerated aging due to acid.  Bathing paper requires great care and may have negative consequences even when done by an experienced conservator.  But, whenever possible it is the first step to reduce discoloration of acidic paper. 

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