Bookbinding and the Conservation of Books
A Dictionary of Descriptive Terminology

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1. A pressing operation employed in handmade papermaking following the initial pressing of the WATERLEAF sheets between felts. Each sheet is removed from the felt, pressed, laid one on top of another, with the other of the sheets being rotated after each pressing, until the desired pressure has been reached. This process of repeated pressing was not a common practice until the 16th century, as evidenced by the roughness and absence of finish of paper made before that time.

2. An old and virtually obsolete method of loosening the hair of skins, by allowing controlled putrefaction to take place in a confined, warm area. It is probably the oldest method of unhairing and possibly is still being used in some countries, particularly for sheepskins (where the hair is often more valuable than the skin). Sweating consists of little more than putrefaction of the Malpighian layer. Because of the danger of damage to the skins in the sweat chambers, unless the process is very carefully controlled (see: RUN PELTS ), its use was discontinued for the best grades of skins following the introduction of safer methods of unhairing (see: LIMING ).

The skins are generally hung from beams in a closed room in which the air is kept warm and humid. During the process a considerable amount of ammonia and amines are generated, which assist in the unhairing action. As soon as the hair slips away easily, the skins are taken from the sweat chamber and placed in saturated lime water, which retards further bacterial actions and causes some swelling of the skins. (79 , 291 , 363 )

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