heat-set tissue
A lens tissue especially prepared for use in
mending tears in paper, strengthening margins, and
for laminating weak or badly torn leaves, by means
of dry application rather than by the traditional
aqueous application. The tissue is made of pure
cellulose consisting of more or less lOO% rag
content, no coating or additives, and a pH of 7.0.
The tissue is not structurally uniform in texture,
consequently there are small random open spaces
and some bunching of fibers. Although its
thickness is presumed to be approximately 0.0015
inch, this can vary from one batch to another,
although it does not normally exceed 0.002 inch.
The tissue is coated on one side with an acrylic
resin. It is applied to both sides of tears, but
to only one side of a weakened leaf, provided that
no adhesive is exposed on the other side. The
tissue is tipped on the leaf with a warm iron
(approximately 100° F.), and then pressed
on firmly through terylene or a textured paper.
The iron is not pressed directly on the heat-set
tissue because this might result in blocking and
may also impart a sheen to the tissue, thus making
it more noticeable.
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