Bookbinding and the Conservation of Books
A Dictionary of Descriptive Terminology

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A method of decorating a book utilizing the capability of a vegetable tanned leather to be molded when wet. After being thoroughly softened in water the leather can be formed or molded into various shapes, which, on drying, retain those shapes with a remarkable degree of permanence. The wet-mold leather can be more permanently set by drying it under moderate heat, the degree of rigidity obtained cuir-ciselé being determined by the drying temperature. A faster method, and one that produces extremely hard and rigid shapes, is to dip the molded leather into boiling water for anywhere from 20 to 120 seconds. This is the process that gave rise to the name "cuir-bouilli." Such a process involves the partial melting of the fixed tannin aggregates in the leather. At a temperature approaching 100C. these aggregates become plastic and can be made to flow and redistribute themselves throughout the fiber network of the leather. On cooling, the fibers become embedded in what can best be called a tough, three-dimensional, polymer network or resin, somewhat similar to the materials made by condensing formaldehyde with substances such as phenol, urea or melamine. The leather actually sets so hard that some books bound in this manner required no boards. The decoration itself was executed by cutting the leather lightly while damp, after which the design was hammered in relief. The shaped leather was then immersed in boiling water, and dried, and the depressions were filled with molten wax so as to preserve the designs.

The molding of leather was known in Saxon times in England, and was widely practiced during the middle ages in both England and on the Continent. The motifs used were generally mythological animals and interlaced foliage. In the late 19th century interest in the molding of leather was revived and used extensively for many objects, including bookbindings. (94 , 236 , 291 )

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