Bookbinding and the Conservation of Books
A Dictionary of Descriptive Terminology

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sheepskin

A soft, porous leather produced from the skins of wooled or hair sheep. It is usually vegetable-tanned and grained in imitation of other (more expensive) skins, e.g., morocco, a process to which it lends itself very well. The term "sheepskin" always indicates an unsplit skin, and is not applied to split sheepskin or SKIVER . Split sheepskin is the traditional material used in producing PARCHMENT .

Sheepskin is somewhat difficult to describe because the individual skins differ so greatly in size, fat content, and general quality of the dermal network. From the standpoint of leather, the closer a sheepskin approaches the hair sheep, the tighter and firmer the fiber network, and, therefore, the better the skin for producing leather. This is the case because the numerous fine wool fibers, as opposed to the lesser number of coarse fibers of the hair sheep, cause the skin to be more open and loose in texture. In addition, the wool follicles are associated with extensive glandular structures, consisting of sebaceous and sudoriferous glands, which also interrupt the dense packing of the connective-tissue fiber network in the papillary layers, as well as the dermis itself.

The grain layer of sheepskin occupies more than a half of the total thickness of the skin; furthermore, in the reticular layer, the collagen fibers are not as compact and run in more closely horizontal directions.

The proportion of adipose tissue to collagen fibers in sheepskin varies widely according to the feeding of the animal. There is frequently an almost continuous layer of fat cells separating the grain layer and the reticular layer. Because much of the fatty tissues is destroyed or removed in the liming, bating, and scudding operations, it is not unusual to find the grain layer and reticular layer of sheepskin leathers separated, sometimes over wide areas. The tanner at times separates these two layers by splitting after liming, and then tans the grain layer for bookbinding purposes, etc., and the reticular layer for chamois.

During the beamhouse operations. the glands in the grain layer are destroyed, leaving the grain layer rather spongy in structure. This, together with the relatively loose and empty structure of the reticular layer, places sheepskin leather in a class by itself.

Sheepskin is a reasonably durable leather if properly prepared and cared for. It has been used as a covering material for books for more than 500 years. See also: LAW SHEEP ;ROAN ;SKIVER ;SMYRNA MOROCCO .

(161 , 207 , 291 , 306 , 363 )




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