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Mass deacidification


Deacidification is a process of treating paper documents for the purpose of neutralizing acids within the paper and to create an alkaline buffer. High acidity levels contribute to the deterioration of paper, causing yellowing, brittleness, and instability.

Sources of Acidity[edit]

Before the mid 1800's, paper was made using cotton and linen rags, with few additives. After the mid 1800's, and due to increased demand for paper, paper was manufactured using ground wood pulp. Wood pulp contains lignin, one of the sources of paper acidity. Other original sources of acidity are the use of alum sizing and bleaching agents during the production process. Paper can also become acidic through exposure to other chemicals, pollutants, acidic inks, and through migration. Acid migration occurs when papers of low and high acidity are placed in direct contact, allowing acid to transfer to the document with lower acidity.

Types of Deacidification Processes[edit]

Deacidification processes are either aqueous (using water) or non-aqueous (not using water). Most deacidification processes use some type of alkaline earth metal to neutralize acidity. This ingredient is carried and placed into the fibers of the acidic material through a gas or liquid carrier (Zachary 2002, 7). Documents can either be treated individually or in groups (mass deacidification).

Aqueous processes cannot be used on documents that are sensitive to water, or that contain water-soluble inks or dyes. Aqueous processes can only be used on single items, and cannot be used on bound documents and books, unless the books are taken apart, treated, and rebound.

Non-Aqueous deacidification processes use solvents or gases to carry the alkaline buffering agent. They are well-suited to treating books and other bound materials because the gas or solvent is able to penetrate deep into the crevices and close spaces of books and treat the material evenly.

Deacidification Processes and Products[edit]


The Bookkeeper process, owned by Preservation Technologies, L.P. (PLTP), is the deacidification process used most often in the United States (Zachary 2002, 9).

Bookkeeper is a liquid-phase process of deacidification that uses magnesium oxide powder suspended in trichlorotrifluroethane. The process can be used on single items and also in mass deacidification. To treat individual documents, the product is lightly sprayed over the document and then is allowed to dry. In mass deacidification, the solution is pumped into a vacuum chamber where the books are mechanically agitated to distribute the solution. (Ritzenthaler 1993, 146).

The success of the Bookkeeper technology led to a trial contract with the Library of Congress in 1995 to treat 72,000 books in two years. Since that time, the Library of Congress has awarded several other contracts to PTLP (Library of Congress Information Bulletin, 2002). Further tests and cooperation with the Library of Congress led to improvements in the technology, and many other libraries have contracted with PTLP for treatment of acidic books.

Wei T'o[edit]

Wei T'o is a liquid-phase process that is primarily used to treat single documents, but can be used in mass deacidification. The process originally treated materials with methoxy magnesium methyl carbonate) through a solvent of methanol and chloro-fluoro carbons (CFCs). Wei T'o associates was later able to create a stable, recoverable solution for use in the process that did not contain CFCs. Certain inks, adhesives, and binding materials cannot be treated using the Wei T'o process in order to avoid damaging them.

Papersave (or The Battelle Process)[edit]

In this mass deacidification process, books are heated and dried, then transferred to a vacuum chamber. An alkaline solution is pumped into the chamber, treating the books. An alkaline buffer is produced in the books through a chemical reaction after treatment. The entire process takes only a few hours, but treated books must remain separate for 14 days until this process is complete.

FMC (Lithco)[edit]

The FMC process was developed by the Lithium Corporation of America (Lithco) and uses carbonated magnesium alkoxide in a freon solution. Like Wei T'o Associates, Lithco has been able to find an environmentally friendly alternative to the freon solution. The process is said to both strengthen and deacidify paper (Porck 1996).

BPA (Book Preservation Associates)[edit]

In the BPA (Book Preservation Associates) method, books are treated with a gas pumped into a vaccuum chamber under pressure. The interaction between ammonia, moisture, and ethylene oxide creates ethanolamines, which deacidifies the material (Ritzenthaler 1993, 146).


The Bückeburg process was developed to deacidify and strengthen single sheets of archival paper. In the process, inks and dyes are fixed, then deacidified by an aqueous solution containing magnesium bicarbonate, then the paper is strengthened with methyl celluose sizing (Porck 1996).

Paper Splitting[edit]

Like the Bückeburg process, the paper splitting process is also designed for treatment of loose sheets of paper, unless books to be treated are removed from their bindings then re-bound after treatment. Sheets of filter paper are pasted to either side of a sheet of paper, then pulled apart to split the paper. The two sides of the paper are then pasted together over a strengthening middle layer using a deacidifying glue (Porck 1996).


Library of Congress Information Bulletin. 2002. Saving the written word: Library awards mass deacidification contract. Library of Congress Information Bulletin 61 (January): 15

Porck, Henk J. 1996. Mass deacidification. An update of possibilities and limitations. Royal Netherlands Academy of Arts and Sciences.

Ritzenthaler, Mary Jane. 1993. Preserving Archives and Manuscripts. Society of American Archivists: Chicago. ISBN 0-931828-94-5

Zachary, Shannon. 2002. Mass deacidification in 2002 and the University of Michigan experience. ARL 224 (October): 6-9.

Further Reading[edit]

15th Annual Preservation Conference.

Mass Deacidification.

Mass Deacidification Publications (Preservation, Library of Congress).

Papersave Mass Deacidification

PTLP : Deacidification.

Saving the Written Word (Preservation, Library of Congress).