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may not now be so extensively practised as in years gone by, it is not, so far as we can judge, very likely to be superseded in the near future.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.
Fig. 3.
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.
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.
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.