Improved Silver Haloid Emulsions for Photographic Purposes.
Year: 1893

page_text: Date of Application, 14th Mar., 1893
Complete Specification Left, 10th Jan., 1894-Accepted, 10th Feb., 1894
PROVISIONAL SPECIFICATION.
Improved Silver Haloid Emulsions for Photographic Purposes.
WILLIAM HENRY PRESTWICH Photographer 744 High Road Tottenham in
the County of Middlesex do hereby declare the nature of this invention to be as
follows:-
My invention relates to an improvement in the making of sensitive silver
emulsions for use in coating glass, films or paper, for making photographic negatives,
transparencies or positives on opal, glass, &c. & the coating of paper for printing
purposes; my object being in the case of negatives, to prevent what is known as
solarisation & halation which characterise negatives made of subjects in strong
contrast if taken on plates coated with emulsion made in the ordinary way from
gelatine only. When for printing purposes on paper or opals, my object is to
impart a matt surface & to transparencies a ground glass effect. These results I
obtain by using in conjunction with gelatine a proportion of starch, arrowroot, corn
or rice flour, or other similar substances.
בד
COMPLETE SPECIFICATION.
Improved Silver Haloid Emulsions for Photographic Purposes.
I, WILLIAM HENRY PRESTWICH, of 744, High Road, Tottenham, 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:-
My invention relates to sensitive silver emulsions for coating glass, films or
paper for photographic purposes, my improved emulsion in the case of negatives
preventing what is known as solarization and halation which characterize negatives,
taken on plates coated with emulsion made in the ordinary way from gelatine only
of subjects photographed in strong contrast; in the case of transparencies
imparting a ground glass effect, and in the case of prints on paper or opal glass
producing a matt surface..
-
These results I obtain by using in conjunction with gelatine a proportion of an
amylaceous substance such as starch, arrowroot, corn or rice flour.
In carrying out my invention I prepare a solution in water of gelatine and
starch or its analogues, this mixture or solution being used in the emulsification of
the silver haloid in the usual manner. In practice I find that the desired matt
surface is obtained by using three parts of gelatine to one part of the particular
starch selected, but these proportions may be varied. To prevent precipitation of
the starch it is advisable after softening the gelatine and starch in water, to raise
the temperature to from 130 to 160 degrees Fahrenheit, this boiling or cooking.
causing a certain amount of swelling of the starch granules and thus rendering
them less liable to be precipitated, than before cooking in the gelatine solution,
but care must be taken not to heat the mixture sufficiently to burst the starch
granules.

page_text: As an example of a chloride emulsion for printing out or for development I give
the following, which I have found to give good results :-
Water
Starch
Gelatine
Citric acid
Recrystallized carbonate of soda
Chloride of barium
Nitrate of silver
Alcohol
-
:-
20 ozs.
200 grains
600
"
50
"
50
"
50
"
÷
150
"
1 oz.
The mixture of water, gelatine and starch to be raised to a temperature of
130 to 150 degrees Fahrenheit and the chloride of barium and nitrate of silver to
be added at a temperature of not more than 110 degrees Fahrenheit. After
filtering the emulsion is ready for use.
The following formula for a bromide of silver emulsion for development I have
found gives very satisfactory results :-
Ammonia nitrate of silver
Nitrate of silver (dry)
Alcohol
200
"
100
33
1 ounce
are added, the bromide and silver at a temperatare of 100 to 110° Fahrenheit.
After filtering the emulsion is ready for coating.
Surfaces coated with the emulsion last described may be developed with any
suitable developer but I prefer to develop with a ferrous oxalate developer as
follows:-
No. 1 Oxalate of potass
Water
Bromide of ammonium
No. 2 Water
Protosulphate of iron
Citric acid
-
-
20 ounces
80
"
400 grains.
Equal proportions of No. 2 being added to No. 1 for use.
80 ounces
""
"
After washing, the film is hardened in a solution of alum having the proportions
of one ounce of alum to sixteen ounces of water, and fixed in fresh hyposulphite of
soda solution containing three ounces of hyposulphite to a pint of water.
If the
prints are not required to be mounted at once they are best blotted off by blotting
paper, otherwise water drying marks are likely to form.
Having now particularly described and ascertained the nature of my said-
invention and in what manner the same is to be performed, I declare that what I
claim is :-
1. In the preparation of silver haloid emulsions for photographic purposes the.
use of a vehicle composed of gelatine and starch or its analogues substantially as,
and for the purposes, described,
2
3

page_text: 2. The manufacture and use of silver haloid emulsions for photographic surfaces
in which starch or its analogues is embodied substantially in the manner and in the
proportions stated.
Deted this 10th day of January 1894.
G. F. REDFERN & Co.,
4, South Street, Finsbury, London, Agents for the Applicant.