Treatment of Acidic Paper

Introduction

When materials contain within themselves the means for their own destruction, independent of outside influences, they are said to have inherent vice. The inherent vice of modern paper (ca. 1850 – present) is that the processes used to create it cause it to be or to become acidic. Acid breaks down the cellulose chains in the paper, which leads to yellowing, embrittlement, and decomposition. The decomposition of cellulose chains that form the basis of paper creates even more acid, speeding deterioration. Once a document has become acidic, the acid will migrate to nearby documents, thereby increasing their acid content. This is called acid migration.

The treatment of acidic paper by mass de-acidification can slow the deterioration of acidic paper, extending its longevity by as much as several centuries (Library of Congress [LOC], 2006).

Why is Paper Acidic?

Prior to the Industrial Revolution, paper was made by hand from linen or cotton rags, and was then sized with animal gelatin (sizing is the treatment of paper that reduces its absorbency and allows ink to adhere to the surface rather than penetrating). All of these ingredients were inert, stable, and unlikely to break down.

With the advent of the Industrial Revolution, machine-manufacturing began to replace hand-manufacturing. Previously, long fibres were used in paper manufacturing; now the fibres were crushed and broken into shorter pieces by rough industrial processes, which meant less stability. Rags became harder to get as poverty increased and people became less willing to throw clothing away. It became common for chlorine to be added to paper to bleach the rags. Animal gelatine sizing was replaced with alum rosum which, when combined with chlorine, produces hydrochloric and sulphuric acids. Toward the middle of the 19th century, the shortage of rags combined with growing demand for paper caused paper-makers to turn from rags to wood pulp, which contain tannins and lignin, both of which break down to form acids (Fitzgerald, 2001). Cellulose fibres in the paper themselves produce formic, acetic, lactic and oxalic acids simply by aging (LOC, 2006).

Treating Acidic Paper

There are several options for treating acidic paper. Extremely damaged or embrittled documents that will not survive de-acidification should be digitized, photocopied or microfilmed. Commercial options include mass de-acidification processes, many of which are available in spray cans from retail or industrial outlets.

Product	Company
BookKeeper	Preservation Technologies, L.P.
CSC Booksaver	Conservación de Sustratos Celulósicos S.L. (Spain)
Papersave	Nitrochemie-Group
Wei T’o	Wei T’o Associates Inc.

It is important to note that de-acidification treatments are not permanent; the alkaline buffer will eventually be used up, neutralizing acid created in the document. Re-treatment will eventually be necessary. Before undertaking any type of treatment, always test an inconspicuous area to ensure that discolouration, residue build-up, or other unwanted side effects do not occur.

Home De-acidification

Richard D. Smith, President of Wei T’o Associates Inc., has provided a useful do-it-yourself treatment for acidic paper. The Simcoe County Archives has successfully used this procedure in the past.

Before you apply this treatment to acidic family treasures, however, examine the document to ensure that it is sturdy enough to survive immersion in liquid. For example, exceedingly brittle newsprint or very delicate tissue paper should not be treated in this way, though lightly embrittled or weak sheets can be treated with this process by placing them on sturdier paper supports or plastic screens.

Ingredients

• 1 quart (764 mL) of club soda
• 2 tsps OR 2 crushed tablets of Milk of Magnesia
• 1 pan, approximately 10” x 15” (25.4 cm x 38.1 cm) and 2.5” (6.35 cm) deep
• white blotting paper
• paper towels

Preparation

• Add milk of magnesia to bottle of cold club soda
• Re-cap and shake gently
• Refrigerate for 10 minutes, then gently shake
• Repeat
• Repeat
• Refrigerate for 30 minute to allow any remaining powder to settle out

Treatment

• Pour the solution carefully into pan, ensuring the settled powder remains in the bottle.
• Put the papers you wish to treat into the solution one by one, fully immersing each one before adding the next, for a maximum of 25 letter-sized sheets.
• Allow to soak for at least 20 – 30 minutes, to a maximum of 1 – 2 hours.
• Move the sheets in the solution several times to ensure constant contact with fresh solution.
• Remove the sheets and allow excess solution to drip off.
• Air dry until sheets are no longer soaking, but still damp.
• Place sheets in a flat layer between blotting paper.
• Press with medium weight (we use sheets of Plexiglas to distribute the weight). Books make good weights.
• If the blotting paper is getting wet, replace it with fresh sheets until the treated paper is dry.

Further Reading

Fitzgerald, R. (2001). Brittle Paper.  Retrieved July 25, 2008, from http://faculty.msmary.edu/fitzgerald/brittle_paper.htm.

Library of Congress. (2006). Deterioration and preservation of paper. Retrieved 28 July, 2008, fromhttp://www.loc.gov/preserv/deterioratebrochure.html.

North East Document Center. (2006). Preservation 101: Preservation basics for paper and media collections.  Retrieved 25

   Jul, 2008, from http://unfacilitated.preservation101.org.

Smith, R. D. (1998). The use of magnesium bicarbonate prepared with milk of magnesia and club soda to protect paper

   against aging. Retrieved 25 Jul, 2008, from http://www.weito.com/use_of_magnesium_bicarbonate_pre.htm.