Bookbinding and the Conservation of Books
A Dictionary of Descriptive Terminology

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A process which is usually defined as "reducing" or "removing." The basic purposes of DELIMING and bating are to remove calcium hydroxide (or other alkali) from the skin, to lower pH, and, of great importance, to treat the skin substance with proteolytic enzymes so as to obtain desired grain appearance in the finished leather. Bating also serves to impart softness, stretch, and flexibility to the leather, while at the same time providing the basis for a clean, smooth grain by loosening scud consisting of hair roots, pigment materials and grease. It also eliminates all traces of the firm, plumped, and swollen state of the skin induced by the alkaline unhairing liquors by bringing the skin into a soft, fallen condition. Today bating is employed mainly in tanning light leathers, such as those used in bookbinding, where drape, flexibility, and softness of handle are of primary importance.

The origin of bating is somewhat obscure but probably dates back to the time when LIMING was not a common practice. It may have been originated by a tanner who noticed that skins badly soiled with dung often produced a softer, stretchier, silkier leather.

As recently as the early years of the present century, the process of bating consisted of immersing the delimed skins in water at a temperature of 35-40° C., and then adding a liquid paste of pigeon or hen dung. The skins were run in this liquor until they acquired a particularly soft, flaccid and silky handle. The finished leather was found to have a very smooth, clean flat, flexible grain and was very soft and stretchy. Considerable variations in time, temperature and quantities were used for various types of leather. The effect of bating was produced by enzymes, which, under appropriate conditions of temperature and pH, are capable of dissolving and digesting some of the protein constituents of the skin. In a properly controlled process they are given only sufficient time for further removal of undesirable interfibrillary proteins, or to modify or weaken those fiber structures which, by binding the collagen fibers tightly together, would cause the grain to be wrinkled and the resultant leather to have no stretch.

Today bating is accomplished by the the use of enzymes extracted from animal tissue, e.g., the pancreas of swine or sheep, or from microorganisms such as molds and bacteria, called respectively pancreatic and bacterial bates. (248 , 275 , 291 , 306 , 363 )

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