An Improved Method of Preparing Photographic Plates of Mica.
Year: 1890

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POM DIE SI MUITICATION:
An Improved Method of Preparing Photographic Plates of Mica.
A communication to me from abroad by OSWALD MOH, of Goerlitz, in the Empire of
Germany.
I, EDMUND EDWARDS, of the firm of Edwards and Co., Patent Agents and
Engineers, of 35, Southampton Buildings, Chancery Lane, in the County of Middlesex,
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, that is to say:
:
This invention relates to an improved method of preparing plates for taking photo-
graphic pictures, and it consists in making the said plates or slieets of mica, which is
submitted to a treatment by suitable agents to remove from the native mica the
mineral grease, before applying the fine sensitive coating of bromide silver gelatine
or the like.
The mica is a mineral which can readily be divided into plates or sheets of extreme
thinness, and it is further known to be as transparent as glass. This very useful
material has not hitherto been generally employed for taking photographic pictures,
for the reason, that the thin coating of bromide silver gelatine or other sensitive
material did not, (or not sufficiently) adhere to the surface of the mica, but became
loose and detached in the bath.
The object of the present invention therefore is to prepare the plates or sheets of
mica in such a manner as to enable the same to hold, fixed and firmly adhering to
them, the thin coating of sensitive material employed for taking the photographic
picture. The obstacle hitherto experienced in fixing the said coating upon the plate
of mica consisted in the mineral grease contained in the native mica, the said grease
preventing the fixed and intimate adherence of the coating. To remove the said
mineral grease, the plate or sheet of native mica according to the present invention
is submitted to a treatment, continued for a sufficient time, of a solution of chrome
alum with an addition of gelatine.
The photographic plates prepared from mica previously submitted to the treatment
described, will hold the thin sensitive coating applied to them, perfectly fixed and
durably.
They resist any fluid employed for developing the picture and any jet or stream of
water directed forcibly against them and at any temperature, without at all impairing
the clear and fine quality of the image.
The plates or sheets of mica offer remarkable and conspicuous advantages over
plates of glass in that they are not liable to breakage, are extremely light, are not
attacked or impaired by changes of temperature, by acids, or chemical agents and
solutions of any of the kinds employed in the art of taking photographs, and they
have besides, a sufficient degree of elasticity to allow of conveniently packing and
transporting them, and a great quantity of such plates may readily he carried on a
journey, without materially adding to the weight of luggage.
The said mica plates also offer the advantage over ordinary gelatine plates or plates
prepared with similar emulsions in not being subjected to deformations or rolling up,
which frequently cause great difficulties in taking a good picture, or even renders it
utterly impossible.
The mica plates, on the contrary, always remain smooth, even and straight, and
owing to their extreme thinness and perfect transparency, they may he readily
employed for taking copies either on the front or reverse side. In general the plates
of mica offer an excellent material for photographic purposes.

page_text: Having now particularly described and ascertained the nature of the said inven-
tion and in what manner the same is to be performed, 1 declare that what I
claim is
The method of preparing photographic plates of mica by applying the sensitive
coating of bromide silver gelatine or other suitable material to the plate or sheet of
mica previously submitted to a treatment by a solution of chrome alum with the
addition of gelatine, or other suitable agent capable of removing the mineral grease
from the native mica and enabling the same to receive in fixed and solid adherence
the said sensitive coating, substantially as and for the purpose set forth.
Dated this 16th day of July 1890.
EDWARDS & Co.,
35, Southampton Buildings, Chancery Lane, London, Agents for the Applicant.