Sheepskin Leather and it's use in bookbinding.

Sheepskin has been used in bookbinding for more than 500 years, and yet today it is maligned as being inferior to all other leathers and thought little of, but as Matt T. Roberts and Don Etherington say in Bookbinding and the Conservation of books. A Dictionary of Descriptive Terminology. "Sheepskin is a reasonably durable leather if properly prepared and cared for." And so I believe it is, I rediscovered the joys of sheepskin by accident, in my search for a lightweight, economical leather, suitable for general quality case work.....Lets have a look at sheepskin and find out a little more about it:

Sheepskin is a soft, porous leather produced from the skins of wooled or hair sheep. It is usually vegetable-tanned and often "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 un split skin.
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, and as has been said, it has been used as a covering material for books for more than 500 years.

Flesher
The inside split (flesh split) of a lamb- or sheepskin, embossed and finished in imitation of grained leather, and used at times for lining the spines of cheaper blank books.

Skiver
The outer grain split of a sheep-, lamb-, or (occasionally) goatskin, vegetable-tanned, and usually from 0.25 to 1.0 mm thick. Skivers are finished in a wide variety of colors and embossed grains, as well as with a plain, smooth surface. At one time skiver was used very extensively for labels of many kinds of bindings, e.g., the red and black labels of law books.

Law Sheep
A natural-colored, vegetable-tanned sheepskin, at one time used for covering law books, but now largely superseded by buckram.

Roan
A variety, or varieties, of leather produced from a superior grade of un split sheepskin. Roan is softer than Basil , and is often colored and finished in imitation of Morocco. The typical roan has a close, tough, long, boarded grain, a compact structure, and is usually dyed a red color. Originally, roans were leathers tanned exclusively with sumac (as were the morocco' s); however, in later years they were often tanned with other vegetable tannins. They were used extensively for covering books from about 1790 until well into the 19th century, but have been seldom used since that time.

Smyrna Morocco
A sheepskin, split and embossed with an imitation Morocco grain pattern.

If a simple case binding is being considered full thickness sheepskin...or goatskin for that matter, is simply too thick for covering smaller books, by which I mean Crown 4vo and smaller, it is not practical to pare down full thickness skins to 1mm / 1.5mm, you can get split goatskins but they are commonly grained and had a sprayed pigment finish which resulted in a shiny hard leather, difficult to pare and rather unpleasant to handle.

Provided you make sure that you are obtaining hair splits and not Flesher's, and if possible that the skins are not subjected to exposure to harmful acids in the tanning process, then I have found that the resultant leather is eminently suitable for general quality case work.

How long will this leather last? A lot depends on the treatment it receives during it's life, but judging by similar books bound in lightweight sheepskin which we repaired or re-bound I would say certainly good for the customers lifetime. And lets face it, the finest book, bound in the finest materials will ultimately decay, it's not just the difference in price of this leather over say best goatskin, it's the fact that right along the line it is easy to work with and needs the minimum of paring and working, all these factors mean that you can make a very respectable leather case cheaply, which means that you can attract customers to a leather bound book who otherwise might be scared off by the price.

For economical leather case work I would seriously suggest you take another look at this oft maligned leather.

References:

Bookbinding and the Conservation of books. A Dictionary of Descriptive Terminology
Matt T. Roberts and Don Etherington

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