Improvements in the Manufacture of Photographic Plates.
Year: 1894

page_text: Date of Application, 17th Feb., 1894
Complete Specification Left, 16th Nov., 1894-Accepted, 22nd Dec., 1894
PROVISIONAL SPECIFICATION.
Improvements in the Manufacture of Photographic Plates.
I, AUGUST ZIMMERMANN, of 6 & 7 Cross Lane, St. Mary-at-Hill, in the City
of London, Merchant, (a communication to me from abroad by The Chemische
Fabrik auf Actien vorm. E. Schering, of 170 Müllerstrasse, Berlin,) do hereby
declare the nature of this invention to be as follows:-
This invention relates to a new process of hardening sensitive gelatine emulsions,
such as bromide of silver emulsion. The hardening is effected by formic aldehyde
(CH,O).
To carry out this invention formic aldebyde solution is added according to the
required degree of hardness, to the bromide of silver gelatine emulsion before
application to the carrier, i.e. the plate or film, taking care to exclude all actinic
rays of light.
This process may also be carried out with isochromatic (colour sensitive)
gelatines, as for instance gelatine emulsions treated with erythrosine.
The formic aldehyde may also be applied to the sensitive or isochromatic gelatine
emulsions after coating the plate or carrier, by dipping the coated plate or carrier
into a weak formic aldehyde solution or exposing it to the action of formic aldehyde
vapours.
The process of rendering the emulsion or finished sensitive plates, isochromatic,
can also be carried out after the treatment of the gelatine emulsion with formic
aldehyde.
The process can also be used for hardening photographic gelatine negative and
positive plates, produced in the ordinary manner; for this purpose they are either
inserted in a weak formic aldehyde solution or exposed to the action of its
vapours.
7th day of February 1894
COMPLETE SPECIFICATION.
Improvements in the Manufacture of Photographic Plates.
I, AUGUST ZIMMERMANN, of 6 & 7 Cross Lane, St. Mary-at-Hill, in the City
of London, Merchant, (a communication to me from abroad by The Chemische
Fabrik auf Actien vorm. E. Schering, of 170 Müllerstrasse Berlin,) 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 a new process of producing hardened light or colour
sensitive gelatine, bromide of silver gelatine emulsion for example, by formic
aldehyde.
As described in the Complete Specification No. 2036 of 1894 a gelatine solution
sets on the addition of a large amount of formic aldehyde to a gelatinous mass,
which is insoluble in water and which cannot be melted (Example add 3 cubic

page_text: centimetres of a 36 % formic aldehyde solution to 100 grammes of a warm 20%
gelatine solution). If very small quantities of formic aldehyde be added to melted
gelatine, the solution sets on cooling but may be easily remelted. When however
the gelatine so treated is allowed to dry upon a surface, an elastic flexible skin
quite insoluble in water is produced.
Now if the formic aldehyde solution be added to gelatine emulsion sensitive to
light in such quantities that the emulsion is after drying insoluble in water, no
prejudicial effect but perhaps rather a favourable effect is thereby produced on the
substance sensitive to light.
To carry out this process small quantities of formic aldehyde solution (more or
less according to the degree of hardness required) are added to for example
bromide of silver emulsion before use, and the emulsion then poured in the ordinary
way, all chemically active rays being excluded, upon plates, paper or other carriers,
such as for example upon the gelatine film described in the Complete Specification
No. 2036 rendered insoluble by formic aldehyde. In the latter case a compound
film is produced, the under film of which is formed of formic aldehyde gelatine and
the upper film of light sensitive formic aldehyde gelatine.
The process also applies to colour sensitive gelatine such as for example bromide
of silver gelatine emulsion, which has been treated with erythrosine.
The finished formic aldehyde plates may also be rendered colour sensitive in the
usual manner.
To produce the before mentioned compound film, the gelatine carrier insoluble
in water described in the Complete Specification No. 2036 is first produced, the
light or colour sensitive silver halide gelatine emulsion mixed with small quantities
of formic aldehyde then poured upon it, it is then allowed to dry and the compound
film either left on the carrier or stripped off it.
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 production of hardened light or colour sensitive gelatine films consisting
in adding small quantities of formic aldehyde to the light or colour sensitive
gelatine emulsion before pouring it upon the plate in such a manner that the film is
after drying insoluble in water.
2. The use of the process claimed in Claim 1 in such a manner that a compound
film is produced by employing a gelatine film rendered insoluble in water by formic
aldehyde according to the Specification No. 2036 and by pouring upon this the
light or colour sensitive gelatine emulsion: mixed with small quantities of formic
aldehyde and allowing it to dry. The compound film thus produced being either
stripped off the glass or metal plate serving as a carrier or left on the same.
3. Rendering the light sensitive gelatine films referred to in Claims 1 and 2
colour sensitive by dipping them into a colour sensitive solution.
Dated this 30th day of October 1894.
AUG. ZIMMERMANN.