COPPERPLATE TRANSFER PRINTING
The Copperplate Press--The Operation--Charging the Engraved
Plate--Cleaning-off and Polishing--Making the Impression--
Useful Notions.
Although copperplate printing may not now be so extensively practised as
in years gone by, it is not, so far as we can judge, very likely to be
superseded in the near future. It is still regarded as a necessary
adjunct to lithography, especially where the amount of commercial work
produced is of any moment.
From a purely mechanical point of view the construction of the
copperplate press (Fig. 3) is of an exceedingly simple character. Its
primary purpose is to produce a heavy and uniform pressure on the plate
during operation.
[Illustration: FIG. 3.]
After being charged with a special pigment and cleaned as hereafter
described, the plate is laid, face upwards, on the iron bed or table of
the press and in contact with the paper, and passed through between two
iron cylinders. These cylinders are so adjusted as to produce an
exceptionally heavy pressure. Such are the simple elements of a process
which, however, requires much closer investigation.
In its application to lithography the following are the only requisites
for copperplate transfer printing.
A stick of prepared transfer ink--whiting, free from grit--transfer
paper, and a plentiful supply of soft rags. Likewise, an iron plate with
a gas jet underneath (Fig. 4), a square of printer's blanket, and a damp
book consisting of twenty or thirty sheets of blotting or other
absorbent paper slightly and uniformly damped.
[Illustration: FIG. 4.]
A good copperplate transfer paper can be made according to the recipe
given in Chap. III., but unless a fairly large quantity is used the
commercial qualities will be found most economical.
Copperplate printing, in its application to lithography, is a simple
operation, but it requires extraordinary care for its successful
execution. The conditions under which lithographic transfers are made
from a copperplate engraving are vastly different from those which
control copperplate printing for ordinary purposes of reproduction.
The engraved plate is first well heated by means of the hot plate
already mentioned. The transfer ink is then _forced_ into the engraved
parts until every line is fully charged, the ink having been previously
enclosed in a double fold of soft rag.
During this part of the operation great care must be taken that the
transfer ink does not burn through overheating, as this would partially
destroy its greasy nature and leave it hard and brittle. The transfer
impression would suffer in consequence, and, though to all appearance
perfect on the paper, it would be weak and ineffective when applied to
the lithographic stone. Such an error of judgment is not at all unusual,
and should therefore be the more carefully guarded against. It
frequently occurs without the knowledge of the operator, owing, it may
be, to his over-anxiety to complete his work in as short a time as
possible.
The plate must now be cleaned, _i.e._ the surplus ink and scum must all
be removed. This may be done before the plate is quite cool, and after a
little experience it will be possible to accomplish the cleansing
process without in any way disturbing the ink in the lines of the
engraving. The rag used for cleaning must be tightly folded into the
form of a pad and kept free from creases. After final cleansing and
polishing with whiting the plate is ready for an impression. The
transfer paper requires damping until it is quite limp, when it is
brought into contact with the inked plate and subjected to a very heavy
pressure. The backing is a woollen blanket, preferably of fine texture;
this ensures perfect contact between the plate and the paper. The plate
is now very slightly warmed to dry the transfer paper, which is allowed
to peel off; this it does very readily if, after a little while, the
corners and edges are but slightly eased.
Oil of tar will effectually remove any accretions of copperplate
transfer ink which may have hardened in the lines of the engraving.
It may be useful also to know that it is possible to use a small
lithographic press in place of a copperplate press, assuming, of course,
that a sufficiently heavy and uniform pressure can be guaranteed. This
is not altogether an innovation, yet it is not a familiar notion.