A New or Improved Method of Treating Canvas, Shirting, Silk, Paper, and like Substances, for the Purpose of Rendering the same Sensitive to Light.
Year: 1893

page_text: Date of Application, 8th Nov., 1893-Accepted, 9th Dec., 1893
COMPLETE SPECIFICATION.
A New or Improved Method of Treating Canvas, Shirting, Silk,
Paper, and like Substances, for the Purpose of Rendering the
same Sensitive to Light.
I, GEORG JACOB JUNK of 84 Steglitzer Strasse, Berlin Kingdom of Prussia,
Empire of Germany, Photographist, do, hereby declare the nature of this invention
to be as follows:-
The present invention relates to a process of treating canvas, shirting, silk,
paper and similar or woven materials so as to make them sensitive to the light and
thus suitable for the reception of photographic reproductions, enlargements or
miniatures in oils etc.
The advantage of the method hereinafter described lies in the fact that the
surface of the material prepared remains practically unaltered and thus the
subsequent treatment with oils or water-colours is rendered easy.
The process taken step by step consists as follows:-
Two separate solutions of nitrate of silver, and bromide of potassium mixed with
iodide of potassium are made in distilled water. A trace of gelatine is added to
the second solution for the purpose of producing an equal distribution of the silver
on the two solutions being mixed together. Both solutions are heated to 28°, that
is until the substances have been completely dissolved, and are then poured together
with the addition of a small quantity of ammonia. A precipitate of bromide of
silver is thrown down, which must not be allowed to coagulate, for which reason
the mixture must, at the temperature of 28° be periodically shaken. After about
an hour the emulsion is ready in the form of a thin liquid.
The emulsion in this form has no stiffening properties and cannot be used for
ordinary photographic purposes. To obtain a proper gelatine emulsion, a quantity
of gelatine must be added as is usual.
According to the present method however, the emulsion as prepared above is
poured into a cold solution of arrowroot made in the meanwhile and which has
been boiled in water until perfectly clear.
After thoroughly shaking the mixture, which remains thin, a sponge is taken and
dipped in, with which the surface of the canvas, silk, paper etc. is washed, either in
a dark room or one supplied only with a red light. After drying, the material is
washed for an hour in water, dried again and is then ready for use. In order to
obviate the washing of the ready material, the bromide of potassium and nitrate of
potassium can be removed from the bromide of silver emulsion before the addition
of the arrowroot by means of a centrifugal or osmose process. The above described
process renders the freezing-action, usually required with the bromide of silver
gelatine emulsion, unnecessary.
The developing etc. of pictures taken on the materials so prepared is proceeded
with in the same manner as with pictures taken on bromide of silver-gelatine-paper.
The advantage of canvas etc. prepared as above described lies in the use of the
same for the reproduction of enlargements or copies of photographs or drawings,
which are to be subsequently painted in oils or water colours.
The artist is spared the trouble of enlarging and drawing the sketch on the
canvas and he can obtain an absolute perfect design for the picture. As the oil-
paint unites intimately with the canvas it is impossible for the picture to peel off,
as often happens by pictures painted on bromide of silver-gelatine-canvas. This
latter has a layer of lime which prevents the oil paint from uniting with the same.
In its use with paper, the above process offers the advantage over the bromide of
silver-gelatine-paper, that it can be drawn upon both with the brush and with chalk,
.....

page_text: which was impossible with the latter paper on account of the impenetrable nature
of the gelative film.
It may be mentioned that the use of starch instead arrowroot produces a similar
effect with however less favourable results.
Having now particularly described and ascertained the nature of this said inven-
tion and in what manner the same is to be performed I declare that what I
claim is:
1.) The herein described method of preparing a bromide of silver-arrowroot (or
starch) emulsion.
2.) The herein described method of treating canvas, shirting, silk, paper etc.
with an emulsion consisting of bromide of silver and arrowroot or starch, for the
purpose of rendering the same sensitive to light.
Dated this 8th day of November 1893.
J. E. EVANS-JACKSON & Co.,
Agents for the Applicant.