Another common mode of copying letters is
by placing a sheet of paper covered on both sides with a
substance prepared from lamp-black, between a sheet of thin paper
and the paper on which the letter to be despatched is to be
written. If the upper or thin sheet be written upon with any hard
pointed substance, the word written with this style will be
impressed from the black paper upon both those adjoining it. The
translucency of the upper sheet, which is retained by the writer,
is in this instance necessary to render legible the writing which
is on the back of the paper. Both these arts are very limited in
their extent, the former affording two or three, the latter from
two to perhaps ten or fifteen copies at the same time.
99. Printing on china. This is an art of copying which is
carried to a very great extent. As the surfaces to which the
impression is to be conveyed are often curved, and sometimes even
fluted, the ink, or paint, is first transferred from the copper
to some flexible substance, such as paper, or an elastic compound
of glue and treacle. It is almost immediately conveyed from this
to the unbaked biscuit, to which it more readily adheres.
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