that has, through
guarding, or excess of sewing, a tendency to be round, is best not
forced to be flat, and a back that would naturally be flat, is best
not forced to be unduly round. A very round back is objectionable
where it can be avoided, because it takes up so much of the back
margins of the sheets, and is apt to make the book stiff in opening.
On the other hand, a back that is quite flat has to be lined up
stiffly, or it may become concave with use.

[Illustration: FIG. 36.]

The method of rounding is to place the book with the back projecting a
little over the edge of the press or table, then to draw the back over
towards the workman, and, while in this position, to tap it carefully
with a hammer (see fig. 36). This is repeated on the other side of the
book, and, if properly done, will give the back an even, convex form
that should be in section, a portion of a circle. Rounding and backing
are best done after the glue has ceased to be tacky, but before it has
set hard.

[Illustration: FIG. 37.]

Backing is perhaps the most difficult and important operation in
forwarding. The sewing threads in the back cause that part to be
thicker than the rest of the book. Thus in a book with twenty sections
there will be in the back, in addition to the thickness of the paper,
twenty thicknesses of thread.

If the boards were laced on to the book without rounding or backing,
and the book were pressed, the additional thickness of the back,
having to go somewhere, would cause it to go either convex or concave,
or else perhaps to crease up (see fig. 37). The object of rounding is
to control the distribution of this swelling, and to make the back
take an even and permanently convex form.

[Illustration: FIG. 38.]

If the boards were merely laced on after rounding, there would be a
gap between the square ends of the board and the edge of the back (see
fig. 38), though the convexity and even curve of the back would be to
some extent assured. What is done in backing is to make a groove, into
which the edges of the board will fit neatly, and to hammer the backs
of the sections over one another from the centre outwards on both
sides to form the "groove," to ensure that the back shall return to
the same form after the book has been opened.

[Illustration: FIG. 39.]

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 a