not hit too hard, or the dent made by the hammer will show after the book has been covered. The back is to be finished with the face of the hammer, the sheets being brought well over on the boards so that a good and solid groove may be made. Each side must be treated in the same way, and have the same amount of weight and beating. The back must have a gradual hammering, and the sheets, when knocked one way, must not he knocked back again. The hammer should be swung with a circular motion, always away from the centre of the back. The book, when opened after backing, should be entirely without wrinkles; their presence being a sign that the workman did not know his business, or that it was carelessly done. Backing and cutting constitute the chief work in forwarding, and if these two are not done properly the book cannot be square and solid—two great essentials in bookbinding.
Backing flexible work will be found a little more difficult, as the slips are tighter; but otherwise the process is exactly the same, only care must be taken not to hammer the cord too much, and to bring over the sections very gently, in order not to break the sewing thread.
Two-edged Backing Boards.The backing boards may be replaned from time to time, as they become used, but boards may be had having a double face of steel to them; these may be used from either side. The edges of the steel must not be sharp, or they will cut the paper when backing. The ordinary boards may also have a face of steel screwed to them, but I prefer to use the wood—one can get a firmer back without fear of cutting the sheets.
There are several backing machines by different makers but they are all of similar plan. The book being first rounded is put between the cheeks, and the roller at the