PRINTING IN THE PRESS.
The etching or damping and rolling-up of the Collotype plate presents
difficulties which are greater even than those met with in the
preparation of the plate. These remarks also apply with equal force
in photo-lithography, and whoever stops at the preparation of the
plates or the photo-lithographic transfer, and leaves the subsequent
operations to be performed by another, should not be considered either
as a collotypist or photo-lithographer. The whole success depends upon
a succession of apparent trifles; many errors it is impossible, or at
any rate difficult, to rectify, and great care should be taken that
nothing is overlooked, or from some trivial cause the whole may result
in failure.
Firstly, remove all adherent matter from the back of the plate, as
the smallest amount of dried gelatine, particle of grit or other hard
matter will suffice to cause the fracture of the strongest glass plate
on the first application of pressure.
=The Etching or Damping Solution= in most common use consists of a
stock solution of five parts water, one part liquid ammonia, three
parts glycerine, and one-tenth part of nitrate of lime. For use add
five or six parts of this solution to 100 parts of water, sufficient
of this being used to well cover the plate when placed in a clean
dish. Another reliable formula is one litre glycerine, 600 cc. water,
chloride of sodium three grammes. Plates may be immersed in these
solutions for a time extending from ten minutes to five hours, or they
may be well flooded with it, wiped off, and dried with blotting paper.
The press having been examined, oiled, and put in thorough working
order, the next consideration will be
=Fixing the Collotype Plate=, which may be performed in several ways.
Immersing the plate in the etching fluid precludes the old method of
cementing it on with plaster of Paris, or glue and whitening, but it
may be fixed by adhesion to a bed of glass or a polished iron plate, or
a special and somewhat complicated frame may be procured for securing
the thick printing plate by means of adjustable clips secured by
screws. Should the printing surface be upon a thin glass adhesion alone
will be found sufficient, a few drops of water causing the printing
plate to adhere to the thicker glass plate underneath. This method
has the disadvantage that it is most difficult to ensure the position
of the plate being in keeping with the mask on the frame. Should the
mask be placed directly upon the gelatine surface of the plate it will
not last many impressions without either tearing or causing damage
to the surface through the formation of creases or wrinkles. If the
picture has to be trimmed without margin, and mounted—either with or
without varnish—the masking is altogether unnecessary. The preparation
of the ink and rollers should next be proceeded with. Supposing the
work in hand to be one of a simple character—say the reproduction of
an impression from a copperplate in black—take a piece of the best
chalk ink about the size of a hazel nut, in an unthinned condition, as
supplied to the printing trade, and with an iron spatula or palette
knife spread it upon the inking slab. Add one-quarter the amount of
middle varnish (refined and odourless), one drop of olive oil, and one
or two drops of best French turpentine, incorporate thoroughly by means
of the palette knife, divide, and apply one-half to the roller. The
next operation is the important one of
=Distributing the Ink.=—A really good leather roller, the handles of
which should be encased with easy fitting leather covers, is most
suitable for the purpose. The ink, by careful manipulation of the
roller, should be gradually distributed over the entire surface of both
roller and slab in a perfectly even and regular manner. Should any
small lumps be observable upon either surface they should be carefully
removed with the palette knife and the rolling and distributing again
proceeded with, as on careful attention to this matter the excellence
of the resulting print greatly depends. The printing plate being well
secured, its moistened surface should be very evenly dried. This is
best effected by means of a roller covered either with fine cloth or
washleather, or a fine soft linen cloth may be used as a substitute.
=Rolling up.=—Apply the inking roller with light pressure to the
nearest edge of the plate, and roll backwards and forwards over its
surface several times; an experienced printer will at once perceive the
condition of the surface. For the first inking a stiffish ink should be
used, as the plate will not then so readily become dirty. By repeated
rolling in different directions, and what is of equal importance,
with varying pressure, endeavour to distribute the ink with perfect
evenness, and with a view of producing a clear and vigorous inking,
which will yield a similar perfect impression. It should be remembered
that
1. A slow rolling with heavy pressure deposits ink on the plate; and
2. Light and quick rolling removes the ink from the print layer.
By modifying the treatment of the plate, and varying the application
of the roller and damping solution, an experienced printer will
demonstrate his power of producing from the same plate flat, weak, and
unsatisfactory impressions, or prints as clear and vigorous as may
be desired. The first application of the ink having been made with a
leather roller, it should be distributed, and the half-tones improved
by the application of a smooth roller, preferably of glue composition.
Without this second inking, it will be found impossible to produce the
highest results in half-tone.
=The Second, or Composition Roller=, must be lightly charged with ink
considerably thinner than that applied in the first instance, the
remarks concerning the pressure applied to the leather roller applying
with equal force in this case. By light, quick rolling, the ink is
partially removed from the plate, while heavier pressure and slower
movement will deposit ink and strengthen the shadows.
When the inking is complete, the frame with the mask is placed in
position. The printing paper, which may be either strong, well-sized
letter-paper, thin cardboard, or the paper known in the trade as “dull
enamel,” cut to a suitable size, is adjusted over the mask, and backed
with a couple of thicknesses of smooth paper. This again is covered,
with the tympan attached to its frame. Push the bed of the press so far
under the scraper that the latter, when pressure is applied, will nip
the plate about one centimetre from the commencement of the picture.
This position has to be ascertained by trial before covering with the
second or tympan frame.
=The Scraper= being regulated so that it will give a sufficient
pressure, pass the bed quickly through the press to the extent
necessary to produce a complete impression. The length of traverse
of the bed during printing can on most presses be regulated by side
screws, or the tympan may be lightly marked. After releasing the
pressure, the bed is withdrawn, the tympan and masking frames thrown
back, and the printing paper cautiously raised by one corner. It often
adheres slightly to the printing surface, and this is usually an
indication of a good plate. The adhesion may, however, at times be so
strong as to tear the paper, or, in the case of enamel paper, remove
the chalk coating. As previously mentioned, the scraper should be
selected of a width somewhat exceeding that of the picture, but never
exceeding that of the glass plate. It may be left plain and moderately
sharp, or covered with leather.
=Damping the Plate= between each impression will usually be
unnecessary, providing a good sample of gelatine is used, and the
damping solution contain a sufficient quantity of glycerine. In cases
where the Collotype plate has been over exposed, or the subject be one
which requires an absolutely white background, damping between each
impression will be absolutely essential. Where it is omitted for any
length of time, the whites of the pictures will always be more or less
degraded or tinted. Should the early impressions not be satisfactory,
patience should be exercised, and by careful treatment with the
roller or rollers, and care in the damping, favourable results will
often ensue after the first few impressions have been pulled. Only
from actual damage to the print layer, or excessive over exposure in
the copying frame, need the plate be placed aside as in a hopeless
condition. The beginner should guard particularly against mechanical
damages in damping; drying and rolling. Lithographers are inclined to
treat the delicate printing surface with the same vigour and energy
that they would apply to the more substantial lithographic stone to
which they are accustomed.
The following directions from “Kleffel’s Manual of Photography” are
to be recommended in printing line subjects, particularly in “glass”
printing direct from the negative:—“The chromated layer of gelatine
must have been submitted to a sufficiently long exposure to ensure it
taking the ink over the whole surface. For the first rolling in of the
plate, the ink should be composed as follows: White wax, 45 parts;
middle varnish, 5 parts; gum elemi, 15 parts; litho ink (about 5s. per
lb.), 20 parts.
“After the plate has been thoroughly rolled in and blackened, it must
be rubbed with a piece of unbleached muslin, previously saturated with
the following solution: 30 parts of ammonia and oxgall (about equal
parts), 30 parts gum arabic, 90 parts water, until the picture develops
perfectly clear. Dry with a clean piece of muslin, and roll in for the
printing proper with ordinary thin copper plate printing ink. Plate
paper, similar to that used in printing from the copper plate, is most
suitable.”
When printing operations are complete, the rollers, printing plates,
and inking slabs should be at once cleaned, as the varnish colours soon
harden and create difficulties.
=Cleaning Leather Rollers= without damaging them requires considerable
practice. They are always scraped with a clean knife, and the
operation should be performed in one direction, to ensure which it
is advisable to mark one of the roller handles. Leather rollers not
in constant use, before being put aside, should have their surfaces
carefully and thoroughly rubbed over with tallow, which must, of
course, be scraped off before the roller is again used.
=Cleaning Composition and Indiarubber Rollers= should not be effected
by means of scraping, but their surfaces should be cleaned with
turpentine, applied with a linen rag free from lint.
=Cleaning the Plates.=—Turpentine is used to free the surface from
every particle of ink, and after the thorough evaporation of the
spirit, the plates should be well washed in water to remove all trace
of the damping solution, dried, and stored in a cool place. It is
sometimes a matter of difficulty to remove ink from Collotype plates
that have been printed from, but a simple method is to pour over the
plate—as in developing a collodion picture—some lukewarm water. This
will dissolve a thin layer of gelatine, and enable one to at once
proceed with the work.