Improvements in Photography.
Year: 1889

page_text: PROVISIONAL SPECIFICATION.
Improvements in Photography.
I, ERNEST HOWARD FARMER, of the Polytechnic School of Photography, 309
Regent Street, in the County of Middlesex, Photographer, do hereby declare the
nature of this invention to be as follows:-
In the ordinary chromium processes the gelatine film containing its silver image
is subjected to several washings fixed and dried. A second gelatine film is prepared
containing a bichromate, and this second film is exposed to light under the silver
image.
The light then sets up a reaction between the bichromate and gelatine wherebythe
latter is rendered insoluble, and as varying quantities of light aretransmitted in pro-
portion to the varying quantities of silver in the first film, the insolubility of the
chromated film is proportional in its different parts to the quantities of silver above
them. The above operation usually requires several days.
I have discovered that when bichromates are brought into contact with metallic
silver suspended in a soluble colloid-such asgelatine, the latter is rendered insoluble
in proportion to the quantity of silver present and I apply this fact to photography.
I proceed as follows;—
The silver image given by the ordinary gelatine dryplate process is immersed in a
strong solution of the bichromate salt; it is then rinsed and dried and becomes
identical with an exposed chromated film. It is subsequently treated in the usual
manner.
Chemically similar reagents may be used in place of the bichromate and organic
bodies similar to gelatine (gum, starch, albumen and the like) can be used in place
of or in conjunction with it.
The bichromate or similar reagent may be placed previously in the film and react
on the gelatine at the same time as the developer sets free the metallic silver.
It will be seen that in my process the developed image is without fixing immersed
straight into a bath of the bichromate the gelatine is already present, and the
metallic silverforming the image acts prefectly in the place of thelight in rendering
the gelatine insoluble.
The bichromate also fixes the plate so far as any further action of the light on it
is concerned.
1000
མཁས་
TFPEEས
COMPLETE SPECIFICATION.
Improvements in Photography.
I, ERNEST HOWARD FARMER, of the Polytechnic School of Photography, 309
Regent Street, in the County of Middlesex, 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:-
The so called chromium processes in photography are based upon the property
possessed by light of decomposing bichromates, and other reducible compounds, in
the presence of gelatine or other colloid substance; whereby in the gelatine (or
other colloid) are induced both chemical and physical changes-chiefly that they
ure rendered insoluble in their usual solvents.
I have discovered that the like changes takeplace when bichromates(or chemically
similar reagents) are brought into contact with silver surrounded by gelatine or
other colloid; that is to say more or less of the gelatine or other colloid is rendered
insoluble in proportion to the quantity of silver present.

page_text: I prefer to proceed as 101lows:-
I prepare dry gelatine films in all respects in the ordinary manner except that I
do not add any hardening material to the gelatine as is sometimes done. I expose
these films in the usual way either in a camera or under a negative or positive.
And if only an invisible image has been impressed the picture is developed also in
the usual way I prefer the iron developer.
Then the plate or surface carrying the film with the silver image upon it, is
immersed in a strong solution of bichromate of ammonia-a suitable formula being
73.
Water
The time of immersion may be one minute.
20
33
The plate or surface is then washed and dried when it becomes suitable for use
in the various ways in which plates with exposed chromated films are now employed.
For example the plate or surface may be used in the following well known
processes:-
1. The plate may be of copper and may be etched; the etching fluid will act
least where the plate is most protected by insoluble matter. A copper printing plate
is thus obtained.
2. The plate or surface may be treated with hot water and then used for printing
by pouring a suitable ink on the surface, laying a paper thereon and expelling the
superfluous ink by pressure.
3. The plate or surface may be used direct for printing by rolling a greasy ink
upon it; the ink adheres to the insoluble parts and is repelled by moisture which
the unchanged parts retain; the inked plate is then pressed against the paper to be
printed.
4. The plate or surface maybe charged with greasyink and afterwashingthe image
may be transferred to a lithographic stone or surface which may then be used in
printing in the well known manner.
In the preparation of the plate chemically similar reagents may be used in place
of thebichromate of ammonia, and organic bodies similar to thegelatine(gum, starch,
albumen, and the like) can be used in place of or in conjunction with it.
The bichromate or similar reagent may be placed previously in the film or
developer and react on the gelatine at the same time as the developer sets free tho
metallic silver but the method above described is preferred.
It will be seen that in this process the chemical reducing properties of silver are
employed, the silver image acting with the aid of the bichromate to render the
gelatine film insoluble.
In this process the metallic silver forming the image acts in the place of the light
in causing chemical change in the film.
Having nowparticularlydescribed and ascertained the nature of mysaid invention
and in what manner the same is to be performed I declare that what I claim is:-
1. The employment in photography substantially as described of the reducing
powers of the silver image produced by light in rendering insoluble gelatine and
like colloid films.
2. In the production of photographicpictures substantiallyas described the process
consisting in obtaining a photographic image on a sensitised gelatine or like film,
exposing and developing the said image whereby silver is liberated in the film and
further causing the film so treated to be acted upon by bichromate of ammonia or
similar reagent whereby the film is rendered insoluble more or less in different
parts and proportionally to the varying action of the light upon the sensitise:l
film.
Dated this 5th dow of Candam Tan 1000