Books that have been hammered so much that they fall straight from the centre towards both sides are called "over rounded"; if, on the contrary, the book is round at the sides and almost straight in the middle the book is called "flat rounded." The latter occurs when the thread used in sewing has been too thin or held down too much (see page 37). Great care must be taken to avoid what is called springing a section—this is generally caused by a break in the glued back; but it is almost impossible to round a book perfectly if the sections are very thick or if it contains many pasted-in plates.
There are now very useful machines for rounding books, also hand machines. The work connected with these consists simply in turning the book a few times, pushing the back up to the rollers each time.
When the book is properly rounded, it is "backed," that is, it is so placed between backing boards that they are away from the back just as much as is required for the groove, the width of the latter depending upon the thickness of the boards; a small thin volume gets thin boards and therefore a small groove; a thicker volume requires thick boards, and, of course, a deeper groove. The made groove should be a little deeper than the board set in it. The book and backing boards are placed in a wooden press, screwing up by hand and once more carefully adjusting. To do this, the press is first placed lengthwise on the table so that one end projects a little over the front edge of the table; the evenness of the rounding is then perfected—one hand at the back and the other at the front edge pushing and adjusting. The better and truer the book has been rounded before laying in the boards the less there will be to do when placed in the press. If the rounding is correct, the head and tail must be examined to see that they are exactly rectangular, for the book may have been knocked untrue, and the evenness of the grooves—which are easily disturbed—is also examined.
Backing and rounding is the most important work as far as regards the appearance of the book when finished; it must be done with the greatest exactitude and requires much practice. Although it is hardly perceptible, yet the great difficulty lies in the book itself being so very easily shifted.
When the book is placed in the press without a fault it is screwed up as tightly as possible with the screw key, and through this the grooves already project over the edges of the backing boards; but a sharp groove can only be obtained by the help of the hammer.
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.
