The art of printing consists in producing impressions from a pattern
or types--cut out and projecting, or engraved and indented--by
smearing the projecting parts or filling up the indented markings
with ink, so that impressions, to any number, and exactly resembling
each other, may be taken from them. Printing is comparatively a
modern invention, although impressing or taking impressions from
seals is one of the very oldest. It is divided into two kinds,
plate-printing and surface-printing. Printing from type or blocks
having the marks to be impressed raised, is called surface-printing,
while that in which the lines or marks are cut in, is called
plate-printing.
Illustration: PRINTING-PRESS.
Illustration: INKING-TABLE.
In surface-printing, when types are used, they are packed up closely
into masses and wedged together in iron frames, so that they form,
as it were, solid blocks; the types or wood-blocks when required to
be printed from are placed in the press, and rolled over by a roller
smeared with printing-ink--this roller is coated with an elastic
substance made of glue and treacle, and resembling India-rubber.
It is worked to and fro on the “inking-table” (a smooth iron slab
fitted with a receptacle for ink), in order that the ink may be
evenly distributed over its surface--a point to which great care
and attention, and no little skill, on the part of the workman, is
directed. The ink, being rolled over the type, covers and adheres to
the surface of the projecting parts. The paper is placed on a frame
turning upon a hinge, and is secured in its place by another frame
brought down upon it. These frames, with the paper, are now turned
down upon the blackened surface of the type, and the whole--paper
and type--passed under the printing press, where, by the working
of a handle, a piece of iron is caused to descend and press evenly
and with great force upon them. On being withdrawn, and the frames
opened, the paper is found to have received a perfect impression,
in ink, of the type upon which it was impressed. This process,
of course, can be repeated to any extent, and as many impressions
produced as may be required.
In plate-printing, the plate is first warmed, and all the engraved
parts are filled in with ink, the superfluous ink being wiped off,
and the surface cleaned bright by using a little whiting (which is
rubbed on the hands), leaving only the indented parts full of ink.
The paper (in a damp state) is then laid on the plate, with a fold
or two of flannel over it, and the whole is carried, by turning the
handles of the press, between two rollers, which compress the plate
and paper together so forcibly that, when removed, the ink is found
to have left the plate and attached itself to the paper, forming an
impression.
Printing is now in very many cases done by machinery, worked by steam
power, so that a very large number of impressions can be produced in
a very short time, as in the case of newspapers, the whole impression
of which (amounting to many thousands) is printed in a few hours.
Printing in colors of various tints, so arranged as to form a
picture, has lately been much resorted to. The usual method pursued
is to print one color, and when that is dry, to print the next, and
so on till the picture is complete; but a machine has been invented
by which many colors may be printed at one time.