The Abbey Newsletter

Volume 21, Number 7

LC Signs Deacidification Contract with Preservation Technologies

Preservation Technologies, L.P. [Limited Partnership] was awarded a four-year contract last fall to provide deacidification services to the Library of Congress. The company will treat a minimum of 216,400 books--and possibly as many as 275,000, according to an LC estimate --during the next four years using its patented Bookkeeper® process.

The new Library of Congress-Preservation Technologies contract follows a joint initiative that enhanced the effectiveness of the Bookkeeper® process, and an earlier agreement that resulted in deacidification of 92,000 books over 18 months.

Under the new contract, Preservation Technologies also is providing onsite services in Library of Congress buildings. The company has three employees, who select books for treatment, pack and ship them to Preservation Technologies, and reshelve them after treatment. The company trains and supervises their workers, and the Library monitors their progress against contract objectives.


Ken Harris, the Preservation Projects Director, has worked with various collection managers to determine which collections are to be processed. Company workers examine each book. Overly brittle books are tagged with a bookmark and left on the shelf. (LC considers book paper having three or fewer half-folds to be too brittle for safe treatment in the vertical Bookkeeper cylinders, though PTLP says that paper that can take only one half-fold can be treated in other ways.)

If there is a question about the pH of a general collections book, workers usually make a small dot with their Abbey pH pens before selecting it. (They mark all books that are alkaline with a white dot on the spine.) They do not generally select materials on coated paper, but many books have some coated plates, and they take these for treating along with the books on uncoated paper.

LC realizes several benefits from this selection process, because it can be integrated with identifying candidates for the LC brittle books program and selecting for repair, among other things.

Treatment process

The Bookkeeper® treatment can be used to deacidify a number of books simultaneously or especially valuable or fragile items one at a time. In a typical mass deacidification treatment, a library ships the books to Preservation Technologies' facility in Cranberry Township, Pennsylvania, where they are placed around the upright central shaft of a large cylindrical tank, held by one or more small plastic coated wires in the book gutter, and anchored at top and bottom. The covers are held open at 90° by rubber bands.

The tank then is filled with a chemical bath composed of magnesium oxide particles (MgO) in an inert liquid carrier, and a dispersant that keeps the particles from sticking together. Unlike water, the liquid "wets" the paper without swelling the fibers and will not dissolve ink or glue, or loosen labels or binding. The particles, because of their size, are attracted more by small-scale electrical surface charges than by gravity. They are invisible to the naked eye.

The submerged books are moved up and down and rotated past subsurface spray nozzles to make sure all the pages are contacted. The process is harmless to books and documents (as long as the binding and text block are structurally sound) and poses no environmental or health risks.

Once embedded in the paper, the magnesium oxide particles combine with water already present in the paper and the atmosphere to form magnesium hydroxide. The magnesium hydroxide then neutralizes the acids in the paper, forming magnesium salts of those acids. The most common reaction is with sulfuric acid, forming magnesium sulfate--in essence, the familiar household epsom salt.

The neutralizing process takes two hours from the time the books begin their bath in the tank until they are ready to be packed for return to their home library.

Quality control

All steps in the process from selection to reshelving are monitored to ensure that the intended results are achieved. Since all methods of deacidification raise the pH of paper to some extent, though no one can accurately predict or control the final pH level, Preservation Technologies measures the success of their treatment by testing for alkaline reserve.

This is done by inserting surrogate paper in roughly 10% of the batches. An acidic bond paper is used for the surrogate testing, because it seems to correlate well with a broad range of papers. This paper is later tested for alkaline reserve, in order to avoid destructive testing of book pages. They also test one destructible test book per week to confirm that the process is working properly.

A further quality control check for alkaline reserve in each batch of books (8 per batch) is made by dividing the weight of the batch into the weight of the MgO used to treat it.

All treated books are marked, like the alkaline books on the shelf, with a white dot on the spine. Treated books also have a Bookkeeper label on the inside of the back cover.


The contract for treating the books is worth 3.3 million dollars. If 250,000 books are treated, this would come to about $13.00 per book for selection, packing and shipping, treatment, and quality control. No pre- or post-treatment conditioning (to lower, then raise, moisture levels in the book) is necessary.

Plans for the future

This article is based on press releases from both Preservation Technologies and the Library of Congress. In its press release, the Library briefly described its future plans regarding deacidification, and gave sources for further information in the following passage.

Congress approved the Library's proposal to negotiate the new four-year contract to deacidify larger quantities of important, endangered books; to incorporate deacidification into the Library's arsenal of preservation options; and to continue to evaluate other mass deacidification processes. The Library continues to encourage other companies with deacidification technologies capable of mass treatment to come forward, if their processes have the potential to meet or exceed the Library's technical requirements....

Staff are ... developing procedures to ensure that information about each deacidified book is part of the Library's bibliographic database. In addition, the Library hopes to perform tests to evaluate the effectiveness of mass treatment of manuscripts and other paper-based materials in nonbook formats.

Given the effective operation of its mass deacidification program over the past two years, the Library will be pleased to act as a demonstration site for managers or technical staffs from other libraries, archives, and cultural institutions who are interested in learning firsthand about administrative and work flow procedures required for mass deacidification programs. Interested organizations should contact Kenneth E. Harris, Preservation Projects Director, Preservation Directorate, Library of Congress LM-G21, Washington, DC 20540-4500. Telephone: (202) 707-1054; Fax: (202) 707-3434; Internet:

Additional information about the Library's mass deacidification program is available at the following Internet address: At that site, select "Research and Testing Online," where a number of publications about deacidification are reproduced, including an informative, illustrated article that appeared in the April 1997 Library of Congress Information Bulletin.

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