Improvements in the Manufacture of Photographic Plates.
Year: 1895

page_text: Date of Application, 19th Apr., 1895-Accepted, 24th May, 1895
COMPLETE SPECIFICATION.
Improvements in the Manufacture of Photographic Plates.
I, WILLIAM HENRI CHARLES CLASEN, Cadettlin No. 7-2, St. Petersburg,
in the Empire of Russia, His Majesty's Photographer, do hereby declare the
nature of this invention and in what manner the same is to be performed to
be particularly described and ascertained in and by the following statement :-
This invention relates to the manufacture of photographic plates and has for its
object the production of a film having a very durable and fine grain. This renders
it possible to take ten times the number of pulls, as is now done without the grain
losing its clearness, further it is possible to print half-tone, dotted or stippled
photographs, devices or signatures, as if from lithographic stones; while the
smudging of the edges of the printing plate is avoided and the covering. devices
hitherto used are thus rendered unnecessary.
These advantages are obtained by applying a lower layer of resinous soap before
spreading the chrome-gelatine. For the production of the latter I prefer to use a
solution of basic chromate of ammonium, which may be obtained from neutral
chromate of ammonium by the addition of an amount of sal-ammoniac equivalent
to the dilute solution.
The action of the resinous soap upon the formation of the grain may be explained
in the following manner.
The resinous soap permeates the layer of chrome-gelatine and forms with the
latter, if bi-chromate of potassium has been used, resinous acid and neutral
chromate of potassium. If the chrome-gelatine after exposure to the light is
treated with water it expands more or less according to the action of the light.
The deepest shadows of the pictorial surface remain contracted, the particles of
resinous acid on the surface not only strongly repel the moisture and thus facilitate
the adhesion of the printing ink, but further attract the ink, during the rolling
on account of their affinity for fatty matter. Therefore as the ink or colour is
more easily retained than hitherto, a more fluid ink may be used than the usual
ink. In consequence I avoid the sticking of the paper, the partial covering of the
printing surface by adhering paper fibre, and the destruction of the grain by
the breaking off of particles of the printing face. Further, even when printing
the richest tones, only small pressure is required, so that the film is not squeezed,
and it is not necessary to pass the print through the press repeatedly.
On the other hand the chrome-gelatine expands considerably at the light parts
of the picture and thus covers the resinous particles which are therefore ineffective.
In consequence the fatty ink is energetically repulsed by the moisture retained by the
raised chrome-gelatine, so that none of the dark parts of the negative, particularly
the edge, take ink, thus avoiding the smudging of the printing surface and the
edge.
The half tones of the pictorial surface are proportioned between the lights and
shadows.
If a solution of monochromate of ammonium is used, which is rendered basic by
the addition of salammoniac, the alkaline re-acting gelatine dissolves at first the
particles of resinous soap. During the drying, the base, salammoniac, of the
chrome salt is evaporated. The resulting acid chromate dissolves the resinous soap
in the above described manner, and the particles of resinous acid remain suspended
in the gelatine.

page_text: The process may be carried out in practice as follows; for instance :-
150 grammes of powdered resin (for instance copal, dammar, shellac, sandarac,
etc.) are brought into a boiling solution of 45 grammes of 'caustic soda in 90 cubic
centimetres of boiling water. To 275 grammes of resinous soap are added 2750
cubic centimetres of boiling water. The resulting solution of ten per cent. normal
resinous soap may be further diluted in practice to the extent of up to 6%. It is
advisable to add a small quantity of alcohol in order to render the solution more
fluid.
A well cleaned plate of metal or glass is covered with the solution (conveniently
by pouring the latter over the plate) at the ordinary temperature of a room
or dwelling. The plate is then dried without the influence of any higher
temperature.
335 grammes of best gelatine are then placed in 2000 cubic centimetres of water,
and dissolved by heating in a water bath. At the same time 100 grammes of
neutral chromate of ammonium are dissolved in 1300 cubic centimetres of warm
water, to which are added 50 cubic centimetres of 10% caustic salammoniac. By
pouring both solutions together the chrome-gelatine is obtained which serves as
printing surface.
The solution is poured, at a temperature of 40° C. on the dry plate in a drying
oven of the same temperature. The plate is then brought again into the oven on
levelled supports, the temperature is then rapidly raised to 55° C. The layer of
gelatine is completely dried, in a suitable drying oven, within an hour, and as a
result is very susceptible to action by light. The plate is then copied under the
negative in diffused daylight. If the negative is normal, the operation will be
completed in about from 10 to 15 minutes and the result is a delicate brown picture
on yellow ground, which contains all details in corresponding proportions. The
plate is ultimately washed in slightly alkaline water until all soluble chrome-salt
(chromate) has been removed.
Having now particularly described and ascertained the nature of this inven-
tion and in what manner the same is to be performed, I declare that what I
claim is :-
A process for the manufacture of photographic plates in which a layer of
resinous soap is applied before the chrome gelatine, which latter contains preferably
salammoniacal chromate of ammonium.
Dated this 18th day of April 1895.
FELL & WILDING,
Agents for the Applicant.