The Abbey Newsletter

Volume 5, Number 2
Apr 1981


Research on the Dressing & Preservation of Leather

by Ellen McCrady
Conservator Aid, Leather Binding Maintenance Project,

Library of Congress, 1979-80. Now with the National Archives.

For a long time, perhaps over a century but certainly since 1925, librarians and collectors have applied dressings to their leather books in an attempt to slow down deterioration, improve the appearance of the leather, and perhaps restore some of its former strength and flexibility. The new generation of technically-oriented conservators have continued this interest. New dressing formulas are invented in every decade and widely discussed, and every so often a new manual or pamphlet appears. Each formula has its own defenders, but the most popular dressings are the ones used by the major institutions. Advice is offered to the librarians and collectors by a small number of experts, very few of whom are directly involved in leather research. Most of the advice is filtered through popular articles and leaflets that do little more than recommend certain procedures, without providing a context to indicate whether those recommendations are supported by research results. Aside from these popular leaflets, there has been little dialog between the generators and the users of knowledge in this area, and as a result the gap between what is known and what is applied has widened.

Some lag must be expected in the transmission of knowledge from one field to another, but when the lag exceeds 30 or 40 years, one begins to suspect that the barriers between the fields may never be overcome without a special effort. I feel that if we do make a special effort at this time, in the 1980's, it will succeed, to the extent that any effort to apply the results of scientific research can succeed.

There is more than a communication barrier involved, however. Unawareness of the barrier is an obstacle in itself. Despite the fact that important decisions are involved, affecting tens of thousands of books and large amounts of money, librarians and conservators do not seem to be aware of the extent to which they are acting without sound technical guidance. The question of which dressing to use seems to have distracted us from the larger, more fundamental questions. Don't we also need to know whether the dressing is having the intended effect on the leather binding? And don't we need to know whether this is the best way to get that effect? Nowadays, if we could, we would take questions like this directly to a staff chemist, or to a specialist in a nearby institution. In this case, however, the questions may hardly seem worth formulating, because there is no one to take them to. The leather chemists are not there anymore.

The Leather Research Literature

Research on leather preservation was once fairly common, and knowledgeable leather chemists were comparatively numerous. There was a great surge of research in the 1930's and 40's. After the Second World War it slowed down as nylon, pyroxylin-coated buckram and other replacements for leather came on the market. Today (ironically, now that conservators are better able to speak the chemists' language) there are only a few chemists left in this country or elsewhere who publish on the subject of leather permanence. There are no signs of a resurgence in the field, aside from the new Leather Conservation Centre in England.

However, the picture is not as bleak as it seems. Before their research funds gave out, the leather chemists in Europe and this country had addressed every important problem, solved (or nearly solved) a number of them, and left behind a large body of literature, a gold mine of information waiting to be taken up, evaluated and used. Most of the questions they worked on are the same ones we worry about today:

  1. What are the chief causes of deterioration in leather?
  2. By what process or mechanism does this deterioration take place?
  3. How can we interrupt or stop it?
  4. How do the several methods of accelerated aging compare with natural aging?
  5. What is the best way to tan bookbinding leather for permanence?
  6. Does dressing make a difference, and if so, which dressing is best?

Leather preservation research was carried out principally by the BLMBA (British Leather Manufacturers' Research Association), the U.S. Department of Agriculture, and the U.S. National Bureau of Standards. It was published principally in the JISLTC (Journal of the International Society of Leather Trades Chemists), JALCA (Journal of the American Leather Chemists' Association) and the Journal of Research of the National Bureau of Standards. There seems to have been little interaction with professionals outside the English-speaking world, but they were in good contact with each other, at least through the literature.

Research on Leather Dressings

The effect of one or several leather dressings on permanence was sometimes studied directly, sometimes worked on as part of a larger experiment; almost inevitably the researchers concluded that the dressing has no preservative effect (Smith, 1964). One study (Wallace, Critchfield and Beek, 1935) found that chestnut-tanned leather treated with sulphonated cod liver oil deteriorated faster than untreated leather. The BLMRA included degreased leather in their long-term study (Elliott, 1969) and found that absence of grease did not make it more prone to decay. Another study (Hannigan, Naghski and Windus, 1965, summarized here) found a slight beneficial effect from certain dressings.

This study compared the results of four different dressings applied at two-year intervals for 34 years on both chrome- and vegetable-tanned leather bindings--a thorough and fair test, likely to show up an effect if there was one at all. Measures of deterioration used were tensile strength, slit tear, soluble nitrogen, soluble sulfate and pH, of which the slit tear test was judged to be the best measure of deterioration.

The four dressings used were 1) vaseline, 2) neatsfoot oil and lanolin 60/40, 3) oil-and-tallow emulsion in water, and 4) a mixture of lanolin, wax, castor oil, sodium stearate and water. The authors conclude that although the dressings provided some protection to all leathers, "their use was not adequate to prolong the life of the vegetable-tanned leather effectively." (They mention this because most leathers for bookbinding are vegetable-tanned.)

Analyzing the figures for these dressings a little further, one finds that although the vaseline did no good at all, and the more complex Dressing #4 was equally ineffective, neatsfoot oil and lanolin did make a difference. One finds that the leather treated with this dressing retained about 10% of the strength (as measured by slit tear) that it would otherwise have lost over the years, judging by the performance of the untreated samples. The oil-and-tallow dressing was about half as effective as the neatsfoot oil and lanolin.

The Benefits of Dressing

There are other reasons for dressing books besides retarding deterioration, of course. Almost all writers agree that it helps keep heavily used bindings from breaking down by making them a little more flexible in the hinges and spine. Few if any writers have explored this question, for instance to determine whether new leather reacts differently than old, or just how much a book would have to be opened and shut before the beneficial lubricating effect on the binding became measurable. Plenderleith (1946) says this added flexibility is the only advantage of dressing, but he still feels it is worthwhile.

Another reason for dressing leather books is the regular occasion it offers for library personnel or conservators to handle, clean and inspect the physical books, a part of curatorial care that is often slighted because of the press of other duties.

There is an immediate change, usually for the better, in the appearance and feel of the leather. This effect is usually quite gratifying, both to the person applying the dressing and to those who handle the books afterwards.

In libraries where even powdery and deteriorated covers are dressed along with the rest, the resulting tidiness is appreciated by both the librarians and the readers. However, because dressings sink into deteriorated leather much more quickly, these bindings usually get heavier applications, whether by accident or on purpose. If care is not exercised, the dressing can "wick" or seep through the spine and hinges into the paper of the text- block. Neatsfoot oil and lanolin, especially the mixture with a preponderance of oil, tends to wick more than some dressings. The Library of Congress Preservation Office has given preliminary trials to an oil-and-tallow dressing designed not to wick, among other things, although the Office has no present plans to dress any powdery bindings.

In some libraries, leather which has become powdery is not dressed at all, because of the danger of wicking. Dust from bindings is controlled (if at all) by consolidating the leather, by removing it from the book, or by rebinding, boxing or enclosing the book somehow.

Dressing Practices at Their Best

In some of the best-care-for collections (e.g. the Rosenwald Collection in the Library of Congress, the Grolier Club Library and the Aberdeen University Library, by repute), dressing is applied as part of a long-standing program of total care. Skilled people are hired to apply it, or trained for the job, and they are likely to receive ongoing supervision. They are expected to exercise their judgment to distinguish between books that should and should not be dressed, to keep the dressing away from the textblock, and to decide how much to apply. Nothing becomes totally mechanical. Standing policies cover whether to wrap the book block first, whether to dress the turn-ins, the method of application, and so on. This level of care represents the best modern version of conventionally accepted practice.

Collections given such careful treatment are in impressively good condition. It is hard, however, to separate the effects of dressing from other factors. Books in both the Rosenwald Collection and the Grolier Club Library (both bibliophiles' collections) must have been selected for acquisition at least partly on the basis of their sound or handsome bindings. A comparatively large number of the bindings must still look more or less as they did when they were acquired, since both of these collections are young as rare book libraries go. In addition, every book in the Rosenwald Collection is said to have been kept in its own box. For this collection, at least, there is no way to separate the beneficial effect of enclosure from that of dressing, since there was no untreated control group, and no systematic observations.

Books as valuable as those in the Rosenwald, Grolier and Aberdeen collections are likely to be not only dressed at regular intervals, but maintained according to conservation principles, which include:

As one might expect, the appearance and handling qualities of books thus maintained are notably better than those not so maintained.

Dressing as Conservation

It could be argued that the dressing of leather bindings is hard to justify in terms of conservation principles, since, first, it has little or no preservative effect. On the other hand, it apparently does no great harm either, provided it is done with care. Certain bindings, in the author's experience, inevitably receive minor damage or disfigurement, but few people seem to be concerned about these changes.

The dressing of bindings is also a largely irreversible procedure, in practice, because the accumulated residue from earlier applications cannot be removed without separating the leather from the book and bathing it with solvents. So far there has been little or no reason to go to this trouble, so reversibility has not been raised as an issue as far as leather dressing is concerned.

There are other questions involving process control, measurement of changes, record-keeping and economics. They are not easy to settle one way or another with the knowledge we have today, but they should all be discussed sooner or later. The literature of leather preservation research and the advice of contemporary leather chemists may be of some help with process control and measurement of changes, among other matters.

Conclusions

The dressing of leather bindings is a popular and well-established procedure, yet there is a fair amount of experimental evidence that it has little or no effect on leather's rate of deterioration. Whether the costs of a dressing program are justified by its benefits is a matter for each library to decide.

References

Bowker, Roy C. "The Influence of Grease on the Deterioration of Chestnut and Quebracho Leathers by Sulfuric Acid," JALCA 26: 667-674, 1931.

Elliott, R.G.W. "Long-Term Durability Test for Bookbinding Leathers: A Review," JISLTC 53: 309-317, 1969.

Haines, Betty. "Deterioration in Leather Bookbindings -Our Present State of Knowledge," Brit. Lib. J. 3: 59- 70, 1977. Condensed in Abbey Newsl., 2: 28-29, 1978. Another description of the BLMRA test described by Elliott (1969). The author states that grease in the outer surface of new leather "has been shown to retard the absorption of sulfur dioxide," but cites no references to support this, and does not mention the good performance of the degreased leather included in the experiment.

Hannigan, Mary V., J. Naghski and W. Windus. "Evaluation of the Relative Serviceability of Vegetable- and Chrome-tanned Leathers for Bookbinding," JALCA 60: 506-518, 1965.

Plenderleith, Harold James. The Preservation of Leather Bookbindings. London: Printed by order of the Trustees of the British Museum, 1946. 24 pp. A manual, by the Chief of the British Museum Conservation Laboratory.

Smith, Richard Daniel. Preservation of Leather Bookbindings from Sulfuric Acid Deterioration. Unpublished MA paper, Univ. Denver, 1964. Carl Wessel (1970) called this "an excellent review of the literature," and quoted all seven of Smith's conclusions, the fifth of which is, "The addition of grease does not protect leather from deterioration by sulfuric acid."

Wallace, Everett L., Charles L. Critchfield, and John Beek, Jr. "Influence of Sulphonated Cod-liver Oil on Deterioration of Vegetable-tanned Leathers by Sulfuric Acid," J. Res. Nat. Bur. Stds 15: 73-77, 1935.

Wessel, Carl J. "Environmental Factors Affecting the Permanence of Library Materials," in Deterioration and Preservation of Library Materials, Howard W. Winger and Richard Daniel Smith, eds., Univ. Chicago Press, 1970. He discusses leather on p. 60.

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Retrieved: Saturday, 25-Nov-2017 09:25:30 GMT