Several kinds of vellum are prepared from calf-skins: "pre-pared" or "artists'" vellum, with a very white artificial surface; "Oxford" vellum, the surface of which is left in its natural state; "Roman" vellum, which has a darker appearance. Parchment is an inferior animal membrane prepared from sheep-skins after the manner of vellum, and is very successfully imitated by vegetable parchment, made by immersing unsized paper for a few seconds in a bath of dilute oil of vitriol. This is used very extensively in France for wrappering the better class of literature, instead of issuing them in cloth as is the custom here.
The cover should be washed with a soft sponge and clean water, to clean off any dirt or finger marks, and to make the book look as fresh as possible. This washing must be very carefully done by going over the surface as few times as possible. This caution applies particularly to the "prepared" vellum, as each washing will take off a certain amount of the surface. It requires some experience to distinguish the flesh and leather surfaces of prepared vellum, but this experience must be acquired, because it is absolutely necessary that the leather side should be outward when the book is covered, for two reasons: the flesh side is more fibrous and adheres better to the boards than the leather side, and the leather side is less liable to have its surface disturbed in the process of washing.
When dry, the parts that are to be gilt must be glaired, and as the glaire will show its presence, or more strictly speaking leave rather a dirty mark, the tools should be worked in blind, and the glaire laid on carefully up to their outer edge. When dry, lay the gold on and work the tool in. Let the tools be only moderately warm; if too hot, they will go through to the millboard, leaving their mark as if they had been cut out with a knife.
As a rule, no very heavy tooling is put on vellum, as the beauty lies in keeping the vellum clean. As the tooling, comparatively speaking, is on the surface, owing to the thinness of the skin, it requires a very competent and clean workman to produce anything like good work on vellum.
Vellum is of so greasy a nature that, if a title-piece of leather has to be put on, it will be a matter of great difficulty to make it adhere properly, unless some special precaution be taken. The best plan is to scrape the surface, where the leather is intended to be placed, with the edge of a knife. This will produce a rough and fibrous ground on which to place the pasted leather. This leather when dry, must be prepared with paste-water and glaire, in the same manner as with other books.