Improvements in Photographic Printing Plates
Year: 1895

page_text: GRAYDON POORE of 7 Norton Gardens Wandsworth in the County of Surrey,
Civil Engineer do hereby declare the nature of this invention to be as follows:-
An ordinary photographic, gelatinous, dry plate is taken, preferably a bromide
of silver plate.
Before exposure, it is immersed in a bath, containing a solution of a chromate salt,
and then rapidly dried. This rapid drying has the effect of reticulating the gelatine,
and so forming a grain suitable for a printing surface, for use with greasy ink, in an
ordinary printers press or machine.
The action of the chromate salt is to form with the silver salt an insoluble double
salt of silver, the effect of the action of light upon which, in the presence of an
excess of chromate salt, is to render the gelatine insoluble, so that when such a plate
is exposed to light behind a negative, those parts which have been affected by light
are rendered insoluble, and when the excess of chromate salt has been washed out,
the whole surface of the film has been rendered comparatively insensitive to light,
so that it may be freely exposed, without being affected.
Plates thus prepared may be printed from with ordinary printing ink, in any
suitable press.
Instead of immersing the plates in a bath, containing the solution of chromate
salt as described above, I may add such salt, in suitable proportions to the emulsion
of silver salts used, in preparing the photographic plates.
The chromate salt I prefer to use, is bichromate of ammonium, and the
proportions vary, according to the effects I wish to produce.
62-13 of December 1905
Improvements in Photographic Printing Plates.
GRAYDON POORE of 7 Norton Gardens Wandsworth in the County of Surrey
Civil Engineer 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 :-
An ordinary photographic gelatinous dry plate is taken a bromide of silver
plate.
Before exposure this plate is immersed in a bath containing a solution of a
chromate salt and then rapidly dried, this rapid drying has the effect of
reticulating the gelatine and so forming a "grain" suitable for a printing
surface for use with greasy ink in an ordinary printers press or machine.
The action of the chromate salt is to form with the silver salt an insoluble
double salt of silver. The effect of the action of light upon a plate thus treated
ID Q27

page_text: in the presence of the chromate salt is to render the gelatine insoluble so that when
such a plate is exposed to light behind a negative those parts which have been
affected by light are rendered insoluble and when the excess of chromate salt
has been washed out the whole surface of the film has been rendered com-
paratively non sensitive to light so that it may be freely exposed without being
affected.
Plates thus prepared may be printed from with ordinary printing ink in any
suitable press.
Instead of immersing the plates in a bath containing the solution of chromate
salt as described above I may add such salt in suitable proportions to the emulsion
of silver salts used in preparing the photographic plates.
The chromate salt I prefer to use is bichromate of ammonium and the proportions
vary according to the effects I wish to produce.
In carrying my invention into effect in one manner I take an ordinary photo-
graphic gelatinous dry plate and immerse it in a weak solution of bichromate of
ammonium in water.
I then dry this plate rapidly by mechanical or any other suitable means.
The plate is now ready for exposure under the photographic negative which it
is intended to reproduce.
After exposure under such negative for a period of time varying according to
the density of the negative the plate is taken out of the printing frame and washed
in water to remove any soluble salts and the process is complete.
It is advisable before printing to damp the plate either by saturating it with a
solution of glycerine and water or with water only.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed I declare that what I
claim is ;
1. The use in the production of photographic printing surfaces of a sensitized
gelatinous plate or film which has been treated, before exposure under a negative,
with a solution of chromate salt.
2. Preparing printing surfaces substantially as and in the manner described.
Dat this 2nd day of October 1806