A New or Improved Process of Producing Photographic Films.
Year: 1899

page_text: Date of Application, 23rd Aug., 1899-Accepted, 14th Oct., 1899
COMPLETE SPECIFICATION.
A New or Improved Process of Producing Photographic Films.
I, JOHANNES MEYER, M.D., of 110, Pennsylvania Avenue, New York, Borough
of Brooklyn, State of New York, U.S.A., 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 process is based upon the discovery of the valuable properties of the silver
phosphates when combined with organic acids, such as acetic, tartaric, citric and
succinic acids. The silver phosphates have so far not been employed for photo-
graphic or other purposes, and the only mention of any application made of them
is to be found in Hardwich's "Manual of Photographic Chemistry." He writes:
"Other insoluble salts, such as the phosphate and citrate, render the paper more
sensitive than when it has been treated with a soluble salt of silver only." The
great value of the silver phosphates consists in their property of forming emulsions
with suitable organic acids which behave in all respects like the well-known
emulsions of the silver haloid salts with albumen, gelatine or collodion. I have
discovered that the silver phosphates, aside from being soluble in ammonia,
phosphoric acid and nitric acid solutions, as was well-known, form solutions with
a number of organic acids, as for instance acetic, tartaric, citric and succinic acid.
But under certain conditions silver phosphates will form in conjunction with an
organic acid a true emulsion.
I have studied the behaviour of silver phosphate towards tartaric acid in this
direction most carefully and, as the tartaric acid-silver phosphate emulsion is
chiefly employed, I will now proceed to give directions how to prepare and how to
use it.
To an aqueous solution of one drachm of silver nitrate a well-diluted solution of
sodium phosphate is added. The resulting silver phosphate is well washed by
decantation and brought to the volume of one fluid ounce. To this silver phos-
phate held in suspension we add five drachms of tartaric acid dissolved in five
drachms of water, at the same time imparting to the containing-vessel a quick
rotary motion. In this way is obtained a white jelly-like mass of a volume of
two ounces, containing a quantity of silver phosphate equivalent to the drachm of
nitrate we started from. It is essential that all the chemicals, including the
water, be chemically pure.
To render this emulsion more fluid, it is either slightly heated, or agitated with
a glass rod or by shaking the bottle. In this state it is used for coating the paper
or other surfaces on which it is desired to print.
The proportions given above are the best for practical use. The preparation
of the emulsion is, however, easier for one not experienced in this special line
of work, by mixing a fluid ounce of silver phosphate with a smaller quantity of
tartaric acid, for instance two drachms of acid in two drachms of water, when
the emulsion will set more readily. When the emulsion is left in its jelly-like
state, crystallization will set in, after some time, while a portion of the silver is
retained in the solution.
Citric acid seems to have the greatest affinity for silver phosphate. Twelve

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drachms of citric acid mixed with one fluid ounce of silver phosphate will produce
a clear transparent solution which has remarkable sensitiveness and qualities.
The emulsion or solution of silver phosphate in organic acid thus obtained is
then applied in any suitable manner to the surface to be sensitized. It may be
applied by means of a soft, flat camel's hair brush to paper, after which it is
permitted to dry. When this sensitized photographic paper is exposed under a
negative to direct or shaded sunlight, a positive picture of great accuracy and
agreeable tone is obtained. When the paper is first coated with albumen
gelatine or any similar substance, a photographic print can be produced in less
time than oy the silver haloids heretofore employed, and not only sunlight, but
also artificial light, can be used for producing a direct print. The photographic
print thus obtained can be toned by any of the well-known toning solutions, and
finally fixed by means of sodium hyposulfite. The print is then washed until no
trace of the hyposulfite is left in the same. In place of paper, any other material
such as wood, celluloid, lithographic stone, silk, cotton or other textile fabric,
and other materials, can be coated with the photographic film, and pictures of
great delicacy and beauty, not inferior to prints on paper, be produced thereon.
The advantages of my improved process of producing photographic films are
that silver phosphates can be employed without the aid of a viscous substance like
albumen or gelatine; that the silver phosphate emulsion or solution can be spread
over almost any surface, like a paint or dye; and that only a very weak solution
of sodium hyposulfite and a short immersion of the prints is required, to remove
the unchanged silver and render the prints permanent.
When the prints are left in the fixing bath for a longer time than a minute,
the sulfuration of the prints will commence, which is induced by the organic acid,
and which will be completed to blackness of the picture in a few minutes more.
Though sulfur-toning is believed to have many objectionable features, the prints
made by the process described do not suffer in appearance if the sulfuration is not
too long continued. The use of albumen will prevent the prints which have
been toned by sulfur from becoming yellow and faded by atmospheric oxidation.
These results were obtained by a number of tests continued through a considerable
period of time. The dominant color of the prints made by the silver phosphate
emulsion or solution is a brown or auburn shade, which darkens considerably with
the drying of the prints. Toning may therefore be dispensed with in many appli-
cations in the arts. When the prints are made on textile fabrics they are
generally brown in tone. but this can be changed in the case of cotton to black
by passing a hot flat-iron over the same, while prints on silk will not undergo this
change. Though the predominating color of the silver phosphate prints is brown,
many of tim show various other tones, and it must be assumed that certain
negatives act as media for the transferring of color qualities and influence the
production of the tone to a certain degree under conditions not yet known. When
à silver bromide emulsion is added to a silver phosphate emulsion, the sensitive-
ness of the solution is so increased that even the light of a common petroleum
lamp is sufficient to produce a direct print. The sensitiveness of the emulsion
is also increased by the addition of a small quantity of citric acid. The solution
of silver phosphate in citric acid, when applied to a plain piece of paper and
exposed under the negative to direct sunlight, produces a print of a very agreeable
bluish tone, which will compare favorably with other prints in accuracy, in the
high lights and in the depths of the shadows.
Paper coated with albumen and sensitized with a silver phosphate emulsion or
solution has great durability and will not deteriorate under climatic influences.
It can be used therefore at any time for printing, without impairing the quality
of the print.
By my improved silver phosphate emulsion or solution positive pictures can
be made with but little trouble and in a very short time. The print is removed
from the printing-frame directly to the fixing bath, to which sodium bicarbonate
is added when the original color of the print is to be preserved. The print remains

page_text: in the fixing bath for a short time and is then freed from any adhering traces of
sodium hyposulfite by washing it in hot or cold water for about five minutes.
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. The process herein described of producing photographic films, which consists
in preparing a compound of silver phosphate and an organic acid, and then apply-
ing said compound to the surface to be sensitized, substantially as set forth.
2. The process herein described of producing photographic films, which con-
sists in preparing an emulsion of silver phosphate and tartaric acid and then
applying this emulsion to the surface to be printed, substantially as set forth.
3. A compound for photographic films, consisting of a solution of silver phos-
phate in an organic acid, substantially as set forth.
4. A compound for photographic films, consisting of an emulsion of silver
phosphate and tartaric acid, substantially as set forth.
5. A compound for photographic films, consisting of an emulsion of silver
phosphate and tartaric acid and citric acid, substantially as set forth.
Dated this 23rd day of August 1899.
TONGUE & BIRKBECK,
31, Southampton Buildings, Chancery Lane, London, W.C.,
Agents for the Applicant.