The practice of applying oils, greases, waxes and other substances to leather hooks in an effort to preserve them appears to be derived from traditional practices rather than 20th century research. None of the serious investigations of leather dressing has shown a preservative effect (McCrady 1981). In fact, there is a great deal of evidence, albeit unsystematic and anecdotal, for specific destructive effects that appear later on, like bloom and mold--effects that have not been observed systematically because of the time lag, lack of previous treatment records, and the large numbers of leathers and dressings involved.
It is true that tanneries add fats to leather as part of the manufacturing process, and that some conservators use dressings on leather artifacts, but these people have controlled conditions, analytical facilities, special training, and good documentation of previous work. These advantages are not available to the libraries and student helpers who carry out most leather dressing programs.
A partial exception to this generalization was the year-long Leather Binding Maintenance Project at the Library of Congress in 1979-1980, which documented the condition and treatments for 8000 leather volumes, 1600 of which received leather dressing. By the end of the project, bloom had appeared on about 200 of these volumes. A trial sample was selected for follow-up (every tenth volume with bloom), and leather chemists at the U.S. Department of Agriculture were consulted about this stubborn problem, for which there is apparently no permanent solution.
It would not be possible now to evaluate the effectiveness of this project, except for the incidence of bloom, even though a careful record was kept of each book treated, because preliminary measurements of the factors we hoped to affect (physical strength, hinge flexibility, dustiness and appearance) were not made, and in fact could not have been made under the conditions. Even if nondestructive test methods had existed for these factors, they could not have been performed in the stacks. A number of photographs were taken before and after, but no measure of appearance was set up, and no photographs were taken to record the final effect after the dressing had diffused completely into the cover and spine, away from the surface. This study was carried out with the utmost care, and it even advanced the state of the art at the time, but it demonstrates that even the best leather dressing projects in libraries are not likely to have the desired effect, and may even disfigure irreversibly the bindings they are supposed to be preserving. The experience of others (Makes, 1984; Raphael, 1983) demonstrates that dressing can also weaken and physically damage the bindings. It does not usually do so, but it is hard to predict with certainty when it will have this effect.
The question then arises, "Why is dressing such a common practice, even among people whose judgement is widely respected?" There is no good answer to that. Established habits and practices are hard to change, and long-term effects are easy even for conservators to overlook or disbelieve, especially if the immediate effect of a treatment is personally gratifying, as the effect of leather dressing is. Soluble nylon, for example, was used in conservation for many years after its dreadful characteristics were documented from every angle in the professional literature (Sease, 1981).
As rational beings we should resist the temptation to do something about even the most appealing deteriorated leather volumes until we know that a remedy exists. Proposed remedies should be thoroughly tested for effectiveness and harmlessness, among other things, and this takes time and money, which are unlikely to be made available in the absence of evidence that any leather dressing has ever been shown to be effective at preserving leather. We should resist the impulse to invent and promote our own "leather formula" to others who know less than we do: this is exactly what the "snake oil doctor" does in a comparable situation, when there is a disease or complaint without a known cure. He gives the people what they are clamoring for, and it makes everyone happy even if no one is cured.
We should also not justify the use of dressing by its long history of use. Traditional practices varied all over the map, and were even less effective at preserving things than folk medicine was at preserving people. Even the British Museum Leather Dressing, which is perhaps the best known, has appeared in several variations; and in the British Museum's own long-term study of durability of bookbinding leather, there seemed to be no difference in durability between the degreased leathers and those that had been dressed (Elliott, 1969).
Here are some early leather dressing formulas, sent in by Susan Swartzburg, Jack Thompson and Tom Convoy, who knew I was collecting them. My hypothesis is that leather dressing was used only for shoes and harness until illuminating gas and the resultant indoor air pollution, along with the use of sulfuric acid in leather tanning and dyeing, started to cause widespread red rot. Then people started treating leather books against the deterioration caused by these influences, using a method borrowed from farms and households, where grease and other substances were used mainly to protect leather against water and the stiffness that results as leather dries. The four formulas follow.
Method of making Leather impervious by Water (1795)
The New England fishermen preserve their boots tight against water by the following method, which, it is said, has been in use among them above an hundred years. A pint of boiled Linseed-oil, half a pound of mutton suet, six ounces of clean Bees-wax, and four ounces of Rosin are melted and well mixed over a fire. Of this, while warm, not so hot as may burn the leather, with a brush, lay plentifully on new boots or shoes, when they are quite dry and clean. The leather is left pliant. Fishermen stand in their boots, in water, hour after hour, without inconvenience. For three years past, all my shoes, even of calfskin, have been so served; and have, in no instance admitted water to pass through the leather. It is also a good Salve --a Basilicon. [From The American Almanac for the year 1796. Pr. Abraham Blaudelt. New Brunswick, N.J. 1795.]
Sizing for Boots and Shoes in Treeing Out (1879)
Water, 1 quart; dissolve in it, by heat, isinglass, 1 oz.; adding more water to replace loss by evaporation; when dissolved, add starch, 6 oz.; extract of logwood, beeswax, and tallow, of each, 2 oz. Rub the starch up first by pouring on sufficient boiling water for that purpose. It makes books and shoes soft and pliable, and gives a splendid appearance to old stock on the shelves.
Harness oil (1879)
Neat's-foot oil, 1 gal.; lampblack, 4 oz. Mix well. [Both entries from The Universal Assistant and Complete Mechanic, containing over One Million Industrial Facts, Calculations, Receipts, Processes, Trade Secrets, Rules, Business Forms, Legal Items, etc., in every Occupation, from the Household to the Manufactory, by R. Moore. New York: J. S. Ogilvie. p. 240-241.]
Notes on Practice (1890)
To polish old bindings, "take the yolk of an egg, beat it up with a fork, apply it with a sponge, having first cleaned the leather with a dry flannel."
Bookbindings become deteriorated in many ways. If they become stiff and rigid, vaseline is good, especially for those bound in calf and morocco. It leaves no trace of its existence to either smell or touch a few hours after its use. [From The British Bookmaker, vol. 10 No. 39, Sept. 1890, p. 10.]
R. G. H. Elliott, "Long-Term Durability Test for Bookbinding Leathers: A Review." J. Int. Soc. Leather Trades Chem., vol. 53: 309-317, 1969. This is an update on the progress of the 1931-1970 study, as of 1965.
Betty M. Haines, "Deterioration in Leather Bookbindings-Our Present State of Knowledge." Brit. Lib. J., 3: 59-70,
1977. Summarized in Abbey Newsletter, vol. 2 #3: 28-29, Dec. 1978. A later report on the long-term British Museum study.
Frantisek Makes, "Damage to Old Bookbindings in the Skokloster Library." Nordisk Tidskrift för Bok- och Biblioteksväsen, 71: 33-57, 1984. Books molded soon after being treated with British Museum Leather Dressing for the first time; vitamin K arrested the mold growth.
Ellen McCrady, "Research on the Dressing and Preservation of Leather." Abbey Newsletter, vol. 5 #2: 23-25, April 1981.
Toby Raphael and Ellen McCrady, "Leather Dressing: To Dress or Not to Dress." Leather Conservation News, no. 2: 2-3, Dec. 1983.
Catherine Sense, "The Case Against Using Soluble Nylon in Conservation Work." Studies in Conservation 26: 102-110, 1981.