OTHER COLLOTYPE PROCESSES.
=The Artotype Company=, of New York, which has acquired Obernetter’s
process, proceed on somewhat different lines to those laid down in this
work, and an abstract of their proceedings is here given as interesting
to those about to experiment. According to Bachrach, “Photographic
Archives, 1879,” p. 66, they proceed as follows:—
[Illustration: _Fig. 9._]
Plates coated with Husnik’s silicate of soda substratum are dried
rapidly in a box heated to 65° C. This causes the solution to
coagulate, the plates are dried in half-an-hour, and as it adheres with
great tenacity to the glass plate, the latter may be at once coated
with the chromated gelatine solution, or it may be kept till the next
day. Before the second coating is applied the plate is well washed and
allowed to dry spontaneously. The drying-box is of wood, 2-1/2 feet
square and 5 feet high, the entire front being a large door, as shown
in the sketch (fig. 9), and the bottom a flat water tank about four
inches deep fitted with two pipes, one to allow the escape of steam,
and the other of use in filling the tank with water. It may be heated
by means of gas or a petroleum lamp. After the bottom of the box has
been accurately levelled, it is covered with a few sheets of blotting
paper, on which are placed the albumenised plates. Occupying the upper
part of the box are adjustable racks, on which other plates are dried.
The box is heated to 82° C., the plates are levelled in their places,
and just sufficient hot chromatised gelatine solution poured on each to
spread up to the edges—not more. The Artotype Co. takes one-third each
of gelatine, isinglass, and the so-called Magdebourg isinglass. Plates
are allowed to remain in the drying-box about 20 to 30 minutes, during
which time the door must not be opened, and particular importance is
attached to the high temperature, reaching even to 93° C., at which the
drying is completed, as it is considered by these means printing plates
of much finer grain are obtained. (The Author believes the temperature
given is much too high, as it would be sufficient, without exposure to
light, to bring about a partial decomposition.) When dry, the plates
may at once be printed under the negative. To etch the plate it is
immersed in a solution of 5 gr. alum in 1 litre of water, rinsed,
allowed to dry, and put in a bath consisting of 150 ccm. of water, 1
litre of glycerine, 300 ccm. of ammonia, 30 g. nitrate of lime. Plates
that have been exposed under the negative too long are treated with a
solution of 20 parts of ammonia, 20 parts of glycerine, and one part of
Venetian turpentine; with this they are flooded. The remainder of the
process is very similar to that already described.
=Seignior Carlos Relvas.=—Vidal publishes the following method of
procedure as that adopted in the studio of this eminent Portuguese
amateur collotypist, where it was introduced by Jacobi:—Very thick
glass plates, finely ground on one side, are used; they are cleaned
with nitric acid, and rinsed in distilled water. The drying box used is
provided with iron bars, fitted with adjustable screws for the purpose
of accurately levelling the plates. Midway between the top and bottom
of the box is an iron plate, underneath which are fitted gas jets. The
doors by which access to the box is gained for the plates consists of
very fine wire gauze, allowing the escape of steam, but preventing the
access of insects. After a thorough cleansing, the plates are levelled
on the adjusting screws, allowed to thoroughly dry, and then coated on
the ground side with the following solution—
White of egg 160 ccm.
Bichromate of potassium 8 g.
Distilled water 480 ccm.
Glycerine 16 drops.
To which is added sufficient ammonia to give the liquid a pale yellow
tint, somewhat less being used where a hard negative is to be employed.
This substratum is filtered, and the plates afterwards coated and
placed upon the levelling screws in the drying box, which is heated to
a regular temperature of 40° C. In about two hours the plates will be
dry, and are then placed, coated side downwards, upon a black cloth,
the back of the plate being exposed to diffused light for half-an-hour.
It is again placed in the drying box, and the second coating, as
follows, applied—
Gelatine 27 g.
Water 400 ccm.
Bichromate of potassium 9 g.
Preparation A 15 ccm.
Preparation B 15 ccm.
Ammonia a few drops.
The preparations A and B are as follow:
A.—Chloride of sodium 1 g.
Water 500 ccm.
B.—Sulphate of alumina 1 g.
Water 100 ccm.
To each square decimetre of surface should be allowed 2 ccm. of the
above solution. The plates are replaced in the drying box, which is
heated to 45° or 50° C. They should be dry in three hours, and are
then ready for printing under a negative in the copying frame. They
are afterwards well washed in filtered water, and allowed to dry
spontaneously in a dust-proof situation. In two or three days the
printing may be proceeded with, the surface having been softened by
allowing the plate to stand for seven hours in the following solution—
Glycerine 500 ccm.
Distilled water 200 ccm.
Preparation C 100 ccm.
PREPARATION C.—Sulphate of magnesia 50 g.
Distilled water 500 ccm.
All solutions are filtered through flannel. From the face of the plate
the superfluous moisture should be removed with a sponge. A very thick
glass plate is fixed to the face of a lithographic stone by means of
glue and whiting, and adhesion is secured between the face of the thick
glass plate so fixed and the back of the Collotype plate by means of a
few drops of water. The whole, so arranged, is placed upon the bed of
the press. Should the prints lose their contrast while the printing is
in progress, they are lightly sponged over with a sponge dipped in the
last-mentioned solution. If this fails to produce sufficient effect,
the plate is first washed with turpentine, and then with the glycerine
solution. Care should be taken to prevent the two liquids becoming
mixed on the plate, to prevent which different sponges and drying
cloths should be used.