To back the book, backing boards are placed on each side (leaving the slips outside) a short distance below the edge of the back (fig. 39). The amount to leave here must be decided by the thickness of the boards to be used. When the backing boards are in position, the book and boards must be carefully lowered into the lying press and screwed up very tight, great care being taken to see that the boards do not slip, and that the book is put in evenly. Even the most experienced forwarder will sometimes have to take a book out of the press two or three times before he gets it in quite evenly and without allowing the boards to slip. Unless the back has a perfectly even curve when put in the press for backing, no amount of subsequent hammering will put it permanently right.
The backs of the sections should be evenly fanned out one over the other from the centre outwards on both sides. This is done by side strokes of the hammer, in fact by a sort of "riveting" blow, and not by a directly crushing blow (see fig. 41, in which the arrows show the direction of the hammer strokes). If the sections are not evenly fanned out from the centre, but are either zigzagged by being crushed by direct blows of the hammer, as shown in fig. 42, A, or are unevenly fanned over more to one side than the other, as shown in fig. 42, B, the back, although it may be even enough when first done, will probably become uneven with use. A book in which the sections have been crushed down, as at fig. 42, A, will be disfigured inside by creases in the paper.
It is a mistake to suppose that a very heavy hammer is necessary for backing any but the largest books. For flexible books a hammer with a comparatively small face should be used, as by its use the book can be backed without flattening the bands. It is well to have a hammer head of the shape shown in fig. 43. By using the thin end, the force of a comparatively light blow, because concentrated on a small surface, is effective.
At fig. 44 is shown an ordinary backing hammer.
Cutting and Attaching Boards--Cleaning off Back--Pressing
The first quality of the best black board made from old rope is the best to use for "extra" binding. It will be found to be very hard, and not easily broken or bent at the corners. In selecting the thickness suitable for any given book, the size and thickness of the volume should be taken into account. The tendency of most modern binders is to use a rather over thick board, perhaps with a view to bulk out the volume. For manuscripts, or other books on vellum, it is best to use wooden boards, which should be clasped. From their stability they form a kind of permanent press, in which the vellum leaves are kept flat. In a damp climate like that of England, vellum, absorbing moisture from the atmosphere, soon cockles up unless it is held tightly in some way; and when it is once cockled, the book cannot be made to shut properly, except with very special treatment. Then also dust and damp have ready access to the interstices of the crinkled pages, resulting in the disfigurement so well known and so deplored by all lovers of fine books.