convex covers
Book covers that are convex in shape because the
book is thicker in the middle than at the spine
and fore edge. Very old books sometimes had covers
that were made convex intentionally, apparently in
the belief that they could hold and support the
leaves better by conforming to the shape of the
text block. The text block was curved because the
early printers produced books that were somewhat
swollen in the middle, the swelling being due to
the sheets being dampened before printing so as to
obtain a better impression. This resulted in the
fibers of the paper in the center part of the
sheet being stretched and separated by the force
of the type. The fibers did not return to their
original conformation following printing,
resulting in a slight additional thickness of the
paper in the print area.
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