barrier sheet
A leaf inserted in a book to prevent the transfer
of ink (and possibly acid substances) from a plate
or illustration to a facing page, as well at times
to elucidate the plate or illustration it
accompanies. The sheet may be a highly sized
paper, so called acid-free paper, or, more often,
glassine paper. It may be loose in the book, sewn
in with the binding, or, in the usual case, tipped
to the leaf it protects. Barrier sheets are
frequently made of an inferior quality of paper,
one which will eventually develop acidity that can
in turn be transferred to the facing text leaves,
weakening them. For this reason, they should be
removed, or, if they bear letterpress and
therefore must be retained, deacidified and
buffered, strengthened (if necessary), and
reinserted in the volume. See also:ACID MIGRATION . (173 )
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