Mass Deacidification Program
The Library of Congress provided leadership in the development and evaluation of mass deacidification processes, through a major initiative that treated approximately 5.5 million books and selected manuscript materials over two decades, starting in 2001. Through a competitive process, the Library awarded a series of contracts for mass deacidification to Preservation Technologies, Limited Partnership (PTLP) of Pennsylvania, to provide book preservation services to the Library using the firm's Bookkeeper mass deacidification process.
Selection Criteria and Procedures
Deacidification treatment was used for acidic volumes located in the Library’s facilities on Capitol Hill. Due to its role as the national library and the official library of the U.S. Congress, the Library was focused primarily on selection of “Americana” for early treatment under the mass deacidification program, emphasizing the selection of endangered volumes from collections that are central to the Library's mission. Screening and treatment has been undertaken for the following LC book classes, which have been approved for deacidification processing by Library administrators, preservation managers, and the LC Collections Policy Committee:
- Class A — General Works
- Class B — Philosophy, Psychology, Religion
- Class C — Genealogy & Biography
- Class D — General History
- Class E — U.S. History
- Class F1-975 — U.S. Local History
- Class G — Geography; Anthropology
- Class H — HJ— Social Sciences
- Class HM—HX Social Sciences
- Class J — Political Science
- Class K — Law
- Class KF — U.S. Federal Law
- Class L — Education
- Class M — Music
- Class P — Language and Literature
- Class Q — Science
- Class R — Medicine
- Class S — Agriculture
- Class T-TX — Technology, Engineering
- Class U-V — Military and Naval Science
- Class Z — Bibliography
Books That Are Not Treated.
Books with the following characteristics are generally not considered for deacidification treatment with the Bookkeeper process:
- Text paper is alkaline or permanent (these books are marked with a white dot on the spine, as are books that are deacidified; in both cases, this mark indicates longevity of the text block)
- Text paper is coated or super-calendered (coated paper is not a high priority for deacidification, due to its alkaline coating) Many art books are on coated paper so for this reason the N class is not part of this program.
- Title is already available in (or scheduled for) microform or digital format, or it is a candidate for future reformatting due to advanced embrittlement of the paper
- Duplicates of a given imprint of a specific title (only one copy of any given imprint is treated)
Candidates for Treatment.
Most books that are deacidified are volumes that are structurally sound enough to be treated in the Bookkeeper vertical treatment cylinders. Books that have binding damage are given conservation treatment in-house and then routed for deacidification treatment. Materials that are too large for treatment in a Bookkeeper vertical cylinder can be deacidified in other ways by the contractor — e.g., horizontally in manuscript-treatment equipment or sprayed.
Books with the following characteristics are considered good candidates for mass deacidification in the Bookkeeper vertical treatment chambers:
Bound Volumes
- Hardbound volumes generally treat better; however,
- Softbound volumes if they are in good condition and structurally sound can be treated (it is critical to determine whether the paper is too brittle to withstand treatment and whether the binding adhesive is too degraded to support the text)
- Plasticized covers will not fully absorb the magnesium oxide and will require wiping off by contractor staff after treatment
Bindings in Good Condition
- No detached covers (boards)
- Leather covers with red rot are OK
- Minor damages (e.g., head cap, head, or tail, as well as minor spine tears and minor hinge or joint damage) are acceptable
Text Block in Good Condition
- No loose or torn pages
- Leaves not overly brittle
- No “blocking” (pages stuck together)
Size Parameters
- Large and heavy books and oversize unbound materials can be treated in Bookkeeper chambers or sprayed.
Quality Controls.
The deacidification process, utilizing magnesium oxide (MgO) to neutralize acid in the paper, takes 1½ hours from the time books are placed in the Bookkeeper cylinders until the volumes are ready to be packed for return to their home library. All steps in the process, from selection to reshelving, are monitored to ensure that the intended results are achieved. The Bookkeeper process meets the Library's basic preservation requirements by:
- raising the pH level of treated paper to the acceptable range of 6.8 to 10.4pH
- achieving an alkaline reserve of 1% to 3%
- extending the useful life of paper (measured by fold endurance after accelerated aging) by over 300%.
Surrogate test papers that are inserted in 10% of the treated batches of books are tested by both LC and the contractor for alkaline reserve in order to avoid the destructive testing (titration) of actual pages from collection books. At LC's request, the contractor also treats one disposable test book per week to confirm that the process is working properly. Test papers and test books are returned each week to LC for additional laboratory testing.
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 left on the shelf during selection screening, with a white dot on the spine. A Bookkeeper label is also attached inside the back cover of each treated book. Currently, all materials treated are documented as treated in the Intergrated Library System (ILS).
Manuscript Deacidification
Preservation Technologies developed new equipment in order to offer deacidification services for loose manuscript and archival materials. The Library contracted with Preservation Technologies to build and install a horizontal treater and a Bookkeeper spray booth in the Madison Building on Capitol Hill. This equipment was used to treat on-site paper-based materials in non-book formats, such as manuscripts, maps, music scores, pamphlets, and posters of a certain size.
