Conservators' Report on the Effects of DEZ on Bound Materials

By Martha-Lucia Sierra and Terry Wallis

The DEZ mass deacidification process has been tested extensively since its beginnings twenty years ago; the Library of Congress has focused testing primarily on bound volumes of non-rare collection materials. In the recent initiative to optimize the DEZ technology, a conservation team was responsible for coordinating, organizing, creating procedures and performing quality control for the 12 test runs, assembling and preparing book test materials, evaluating the materials after processing, and for interpreting and preparing written reports on the evaluation and test results. The group included a conservator in private practice, who was hired due to the size and complexity of the project.

Conservation Considerations/Examination of Treated Materials

From the conservation point of view, a successful mass deacidification procedure for non-rare collection materials is based upon physical and chemical as well as aesthetic considerations. Regarding the effect of the DEZ process on the stabilization of the object, the conservator can only evaluate the physical condition by visual examination. Ideally, this information would be used in conjunction with mechanical and chemical testing performed by a materials scientist. While physical and chemical stabilization can be measured in an objective way, aesthetic considerations are more subjective and are evaluated using olfactory, tactile, and visual criteria to determine the degree of acceptability of side effects resulting from treatment.

The aesthetic criteria originates from the conservator's orientation towards rare materials, but actually seeks to set a realistic base that may be applied to non-rare collection materials. For rare materials (not subject to mass deacidification), any damage caused by a process defines the treatment as unacceptable. The conservator will accept some level of alteration in non-rare materials, as a direct result of a mass treatment. However, the mass deacidification treatment should be non-invasive and non-altering, the "acceptable" change being minimal.

Visual examination of the object can be performed before and after the treatment with a checklist. The checklist will serve to confirm the before-treatment condition --for instance, that the binding appears unaffected; there are no dimensional distortions, stains, or non-uniform coloration of the covering material; no alteration or oozing of the adhesive at the head and tail of the spine; no lifting of original previously adhered materials; no iridescent rings on the covers, textblock and/or endpapers; no blocking, cockling, or warping of the textblock; and that the ink or other writing media is uniform, intact, and has not moved.

Physical handling will reveal any change in the feel of the covering material, distortion of the boards, swelling and/or cockling of the textblock, blisters in the plasticized paper covers or in labels, etc. The DEZ process can cause some materials to become friable as well as affect some types of adhesives, plastic book covers, and photographic materials. The mechanical examination, to be performed by a materials scientist, will assess any effects that the treatment process may have on the nature and longevity of the composite structure that comprises a book.

The olfactory criteria, like the tactile and visual ones, form part of the physical examination. Origin or cause and control of odor became one of the focal points of the investigation of the DEZ process. The conservation lab at the Library evaluated odors in books treated with DEZ, using the following criteria:

Since the test results varied due to the changes in the DEZ test runs specifications, odors in the books also changed. The Preservation Directorate compiled data from an Odor Panel, consisting of 3 conservators, who evaluated the smell of DEZ-processed books. Each member of the Odor Panel worked individually, using three control books to help in the verification of test odors. The panelists used two scales of odor for rating the DEZ-treated books against the control books: the first scale is the "intensity" scale, and the second one is the "descriptive" scale, which identifies different kinds of smells.

A second team of evaluators consisting of Library managers, comprised the Mass Deacidification Assessment Panel. They evaluated groups of 100 DEZ-processed books at a time, rating the physical condition and odor of the books. Once evaluations were completed, the processed books were shelved in a Library environment. Odor re-evaluations occurred at one and three month intervals after the first odor evaluation.

Results of the 12 Test Runs

Each run was evaluated to determine necessary changes in the specifications for subsequent test runs. The first two runs used virgin white paper books without covers, inks, adhesives, or other foreign substances. Resulting from these runs were a noticeable odor with a temporary sweet smell, which disappeared after the books had been aired at room temperature for several months, but leaving behind the classic DEZ odor, which also decreased in intensity with the passing of time.

In runs 3 through 5, the run specifications were altered in an effort to control odors in treated books. The permeation time was reduced from 10 hours to 4 hours to shorten the exposure of DEZ to the cellulose. In run 4, the books were separated in two batches: one batch would not receive post-treatment rehydration, while the second batch would. Odor was lower in the books that went through the post-treatment step.

DEZ treatment at room temperature (85F) in laboratory research produced acceptable odors in treated materials. This lower temperature threshold became the target for improving the odors in treated books. Runs 8 though 12 aimed at lowering book and DEZ circulation temperatures to reduce odor and physical damage in treated books. In earlier runs, the DEZ process exhibited certain limitations -- it occasionally affected certain types of plastics, adhesives, artists' colors, book covers, photographic materials, copying processes and coated paper of the non-rare collection materials. By the end of the R&D initiative, however, stable permeation operations were achieved, and lower DEZ circulation temperatures during the permeation step appeared to result in lower odor levels and very little physical damage to treated books. Also, exposing the books to three days of post-treatment in a separate chamber lowered the odor level of the treated books. In review, Runs 11 and 12 were the most successful.

The conservators' general sense is that the majority of book types processed in these 12 runs pass visual examination, appearing to exhibit little or no damage resulting from DEZ treatment. The conservator odor panel found odors in treated books to be more pervasive and less acceptable than did the deacidification assessment panel that was comprised of LC managers.


1 Ann F. Clapp. Curatorial Care of Works of Art on Paper, 3rd edition. (New York: Nick Lyons Books, 1987), 25.

2 Chandru Shahani, Ph.D., interview by author, 17 May 1994.

3 Preservation Technologies, Inc., "Health and Environment Issues" (Unpublished report, August 1993), 2.

4 Baetcke, Karl P. Letter to Kenneth E. Harris, September 12, 1994.

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Timestamp: Thursday, 04-Nov-2010 14:30:44 PDT
Retrieved: Friday, 24-Nov-2017 16:24:46 GMT