Pig skin can be recognised by its smooth hard surface, strongly pitted with bristle holes. It is closely imitated in inferior leather, bristle holes and all, and when such imitation is actually on a book it is very difficult to detect, but if in skin form it can easily be recognised. In real pig skin the bristle holes penetrate right through the leather, and show quite as much at the back as they do in the front, whereas in the imitation they show little, if at all, at the back. Also the back of real pig skin is of very firm, close texture, but the imitation shows a more or less woolly or loose grained back, as it is generally made of sheep skin. French binders have never favoured pig skin much--it is not dainty enough for them. Sheep skin has always been a favourite leather for bookbinding, but it is not a fine leather and has never been used for first-rate binding. It has, however, been more worked up than anything else into imitations of fine leathers. The imitation of fine leather in inferior sheep skin has been for a long time a very important industry, and it is one which is still with us. All fine leathers show a particular and well known grain on their surface, but the most largely imitated is that of goat skin or morocco. In a well grained skin of morocco, the beautiful grain is strongly marked, whether it be “pinhole” or “straight”--so strongly marked indeed that a cast of it can well be made in plaster of paris. From such a cast a metal die can be made, and when this die is strongly pressed upon a prepared piece of sheep skin, which will take an impression extremely well, the result is that a surface is produced which is so exactly like a piece of morocco that even a leather expert may be, and often is, taken in by it. In course of time, however, the impression flattens out, and the fraud betrays itself. When such a stamped sheep skin is new on a book, and finished with gold, no one would for a moment suspect its genuineness, but if in skin form, the back of the leather will at once betray it. Real morocco has a hard close grain, but the back of the imitation will show a loose soft texture. Other leathers are imitated in the same way: pig skin, lizard skin, and others; and although there has been, and still is, much of such imitation used in the matter of bookbindings, there is still more of it used in the furniture trade. But putting aside these base uses of sheep skin, it has a very fair record to show on its own unaided merits. Many early Italian bindings, good ones, were made in sheep skin; certainly it has not lasted well, but no doubt when new it was pleasing enough. In England, many of the early fifteenth century panel stamp bindings were made in sheep skin, not quite satisfactory now, but also probably well enough when new.