QUALITY OF GLASS SUITABLE FOR PHOTOGRAPHIC PURPOSES AND HOW TO
PREPARE IT.
Mr. Hardwick, than whom there can be no more faithful or competent
guide, says that much care should be taken in the selection of glass
to be used in the production of photographic negatives.
Window glass is always unsuitable, because of its inferior quality,
having scratches upon its surface and air bubbles in its substance,
each of which causes irregularities, as well in the negatives as in
the subsequent printing; also the squares are seldom flat so that
they do not lie true in the holder, and hence a part of the image
may be out of focus; and also they are extremely liable to be broken
by compression in the printing frames.
Formerly many photographers used a thin plate glass of very fine
quality, but of late years the great demand for glass suitable for
such purposes has made it possible for the manufacturers to prepare
a cheaper quality, well adapted to the uses of photography.