Bookbinding and the Conservation of Books
A Dictionary of Descriptive Terminology

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leather dressings

Substances, or mixtures of substances, applied to leather bookbindings to prevent or retard deterioration, preserve, and, to limited extent, restore flexibility to leather. Over the past one hundred years or so a great number of different leather dressings of varying degrees of effectiveness have been used to impart new life to deteriorating leather. These treatments have ranged from simple paste-washing and/or coating with varnish to more-or-less carefully formulated and tested preparations. Most of the latter contain an oil which may be of animal, vegetable, or mineral origin, in order of probable decreasing relative value as preservatives. While such dressings may preserve, and to some extent restore, the flexibility of the leather, they cannot prevent chemical decay, nor can they restore leather that has become decayed because of chemical influences.

The majority of leather dressings contain lanolin as their principal fatty component. Lanolin has sufficient capability to exchange water with the surrounding atmosphere and to maintain relatively long-term flexibility and softness of HANDLE in the leather. Most dressings also contain one or more of the following substances: beeswax (or some other harder or softer wax, such as candellila, spermaceti, carnauba, etc.), cedarwood oil, n-hexane (or benzene), potassium carbonate, potash alum, isopropanol (or ethanol), thymol (or p-nitrophenol or o-phenylphenol). and neat's-foot oil. Beeswax is said to give body to the surface of the leather which can then be polished to impart a glossy finish. (See further comments below concerning the use of wax.) Cedarwood oil provides protection against mold growth and insect attack. The n-hexane or benzene acts as a solvent to get the lanolin into the leather, but according to some authorities, usually evaporates so rapidly that it actually is of little benefit. Furthermore, such hydrocarbons are flammable as well as toxic, and benzene is extremely toxic. The alcohols, isopropanol and ethanol, are sometimes added to a dressing to promote the penetration of the lanolin and also to permit the use of a wider range of organic substances—e.g., fungicides, such as thymol—to be included. The metallic salts, such as potassium carbonate or potash alum, are said to help in binding the fats to the leather fibers. Neats'-foot oil is another fat used to lubricate the fibers of the leather.

The use of hard waxes in leather dressings is very controversial. Some argue that their use reduces the danger of penetration of harmful atmospheric gases into the leather, e.g., sulfur dioxide, which can be converted into destructive sulfuric acid. Others, however. contend that wax decreases the capability of the lanolin to exchange water with the surrounding atmosphere and that the lanolin itself will reduce the ingress of harmful gases. It is also argued that the wax causes treated volumes to stick together on the bookshelf, and even worse, that repeated applications may result in building up a heavy wax surface which eventually cracks and flakes, taking pieces of leather with it.

A simple, economical, and certainly widely used, dressing consists of a mixture of 60% neat's-foot oil (20° C, cold test) and 40% anhydrous lanolin, or 60% lanolin and 40% neat's-foot oil, depending upon the temperature and relative humidity in the area of use. This dressing offers some important advantages over many other preparations. It is (relatively) less expensive, easy to prepare and apply, non-toxic, non-flammable, and contains nothing, insofar as is known at this time, that could possibly damage the leather. See also: P.I.R.A. TESTED ;POTASSIUM LACTATE .

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