The best calfskins for bookbinding purposes are prepared by tanning in oak bark or sumac tanning liquors. Its freedom from grain defects makes calfskin suitable for finishing in delicate shades of color. It may be finished rough or smooth, the latter being more common, and, as it may be without any noticeable grain pattern, it may be tooled with very little preliminary blinding in.
Books which are full bound in calfskin may be described as being diced, grained, marbled, mottled, scored, sprinkled, stained, or tree, according to the form of decoration used. In addition, special styles are known as divinity, antique, law, reverse, or rough calf.
Calfskin has been used as a covering material for books since 1450, or even earlier, and, up to the end of the 18th century, it was a common bookbinding leather. Thereafter, various forms of sheepskin, and later cloth, replaced calfskin as the most commonly used bookbinding material.
There are two distinct views concerning the durability of calfskin. Some contend that because the skin is from an immature animal, the leather made from it cannot be durable, even when carefully selected and tanned, because the fibers of the skin are not fully developed. Furthermore, there is the argument that, since the skin is very soft, it shows scratches and mars too easily, and, when used, the book must then be varnished or kept in a box. Others, however, argue that if the skins are selected carefully and tanned very slowly in oak bark or sumac, calfskin makes a quite durable leather capable of withstanding considerable wear.
Physiologically, calfskin is not nearly as weak as its detractors maintain. Although the fiber network is indeed lacking the depth of cowhide, the fiber bundles are reasonably stout and contain numerous finer fibers which are long, highly ramified, and of high tensile strength. This is because, in any young animal, the connective tissue, i.e., skin, develops more rapidly than some other parts of the body, such as the muscles. The dermal network of calfskin is therefore reasonably well developed and exhibits remarkable strength and toughness. In addition, there is no denying the fact that there are calfskin bookbindings that have come down to us in their original bindings; many are several hundred years old. In as much as the durability of calfskin before the 18th century was not in doubt, it may be that it was the lowering of tanning standards that resulted in less durable calfskin. Furthermore, the bleaching methods employed to produce light-colored skins, as well as the techniques of decorating calf bindings with acid and other chemicals to produce mottled-, sprinkled-, and tree-calf effects were probably the major reasons for its reputation of insufficient durability. See also: SLUNK ; TREE CALF . (207 , 291 , 351 , 363 )