The hammer, however, must not be used blindly on the back, but by lightly knocking, blow by blow, the first and last 4-6 sheets must be brought over the edges of the boards. This done, the whole of the back is well pasted, and after remaining thus a short time it is then rubbed with the point of the hammer along the sheets until all superfluous glue is soaked and scraped off. With a handful of paper cuttings the back is rubbed smooth and clean. The use of a toothed cachir iron is strictly forbidden, but the round side of this tool may be used instead of the hammer.

For backing, we have also a useful machine-the backing machine. For small shops it is made for clamping only, and the making of the groove is done with the ordinary hammer. For large shops this machine has a roller going right across the back which forms the groove down each side.

Valuable books are either trimmed at the front and at once backed or they may be backed before trimming. This is generally done with bulky books, as they are liable to throw out a section, and this danger is lessened by backing first. The work of backing remains the same. If the fore-edge has already been trimmed, care must be taken that the grooves do not suffer during trimming after backing. One way of affecting this is to lay the book on a special cutting board with the edge up to the groove, or by making use of the arrangement on the clamp already described, and adjusting the groove of the book to the blocks fixed on the clamp.

Should the fore-edge not have been cut, the book must again be knocked straight after backing; to do this a strong cord is tied round the book about It cm. from the back, the book is then laid upon a firm bed, and the back again knocked straight; this work is called "tying up."

It facilitates the work if the book is taken up and lightly held in the left hand whilst the right holds the hammer and knocks the round inwards until the book is once more square.
The squared book is now trimmed, and it is not until the trimming is finished that the cord is loosened. In pressing, several volumes of the same size can be done in the hand press at one and the same time.

< Cutting, Rounding and Backing part 3