Improvements in Photographic Stripping Films.
Year: 1899

page_text: Date of Application, 12th Sept., 1899-Accepted, 11th Nov., 1899
COMPLETE SPECIFICATION.
Improvements in Photographic Stripping Films.
.:
J
I, ALBERT HOFMANN, Chemist, of 9, Altenbergerstrasse, Cologne, in the
Kingdom of Prussia, 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:-
-
Celluloid and gelatine skins, so-called films, as well as negative papers, which
previous to copying are made transparent by being saturated with an, oil or
vaseline solution, are now regular articles of commerce as a substitute for the
heavy and fragile dry plates. Celluloid films, on account of their electric pro-
perties and their containing camphor, cause haziness and other faults. Gelatinė
films are very much influenced by moisture. Moreover their preparation is
very difficult and expensive. Oiled negative paper copies slowly, and some
time elapses before the paper becomes so transparent that the structure of the
paper is no longer visible when copying.
The oil occasions spots on the copying paper, and by gradually percolating
into the negative film decreases the usefulness of the negative for further
copying.
Films, which can be drawn off from a paper etc. foundation, are up to date
produced by inserting a layer of soluble gelatine between an insoluble prepared
gelatine film and a paper foundation, which soluble layer before the develop-
ment and the production of the positive, is dissolved by hot water and thus
separates the negative from the foundation.
These negative papers become after a time worthless, as the chemicals such
chrome-alum, or formaline, which make the prepared gelatine insoluble,
soon make the soluble gelatine also insoluble.
as.
Another kind of negative paper to be detached was made by impregnating
warmed, gelatinised alumnised paper, which was tensely stretched over a glass
plate, with wax. All surplus wax had to be avoided, and a film, sensitive to
light, was poured on after the preparation.
After admitting the light, developing, and washing, the picture is first of
all strengthened by the pouring on of gelatine, so that it may independently
serve as a negative after being liberated from the paper foundation... This
freeing is achieved by moistening the reverse side of the paper with turpentine,
and then after a short time undertaking the separation with a very thin paper
knife.
By this and the following processes, the negatives separate with great diffi-
culty and seldom without distortion.
A third method of preparing such negative papers to be drawn off, consists in
spreading wax or a stearine solution over asphalt (bituminised) paper; after the
evaporation of the means of solution, a gelatine emulsion is laid on. The
separation of the picture layer from the foundation takes place by pouring a
gelatine solution over it, whereby on the one hand the negative is strengthened,
and then after drying, the completed negative rises of its own accord. Even
here, the separation must be aided by mechanical means, whereby distortions
can only with great difficulty be avoided.
A lately described process completes the work of separation of the negative
layer from the paper in a dry condition, by sticking the gelatine layer to the
paper with brittle resin, and after the photographic operations (or even during

page_text: the same) freeing it at one corner and drawing it off. This last method has a
great drawback which much diminishes its practical utility, in that the picture
is too easily freed from the foundation, even without the wish of the operator,
whereby the completion of the picture is much obstructed if not even put in
jeopardy.
For the same reason, the papers can never be used as films to be rolled up
because even by unrolling the same, a separation takes place between paper and
film.
The following process permits of the manufacture of negative papers that can
easily be removed, and which exhibits none of the shortcomings aforesaid, but
rather produces an article which promises a general use, a light and easy
handling, and sure results. Smooth, well gummed, even baryta-weighted or
similarly prepared papers, or woven materials or other flexible bodies serving
the purpose, are coated either on one side or both sides with substances soluble
in alcohols, ethers, or benzines, such as resin alone or in combination, but at
all events not made brittle, but softened through being dissolved in fatty oils
or turpentines. The best results are obtained with simple solutions of shell-lac,
gum-sandrach, or mastic with the addition of fatty or drying oils, e.g. castor oil,
also with turpentine or the common pine-tree resin with suitable additions to
make and to maintain the product soft and ductile.
Just as good are the (in the alcohols etc.) soluble albuminous bodies of cereal
origin such as (gluten proteïne) vegetable gluten.
After this film is taken up and has dried on, one applies a gelatine coating
to which is added a hardening medium, alum, chrome-alum, or the like. With
a suitable concentration one can get a sufficiently thick coating in one operation.
otherwise one must repeat the operation often enough to give the final product
the requisite strength in order that it may act as independent negative without
any later strengthening. Under certain conditions gelatine can be applied to
both sides of the paper, and after being dried, coated with a layer sensible to light,
whereby it is rendered serviceable for using on both sides. In this case, the
original paper must be blackened. The laying on of the sensitive sheet is
accomplished in the well-known manner, as well as the development, fixing,
and washing of the negative after exposure.
Before the negative is dried, it is placed for a few minutes in a spirit bath,
after which the paper easily loosens itself from the foundation. In order that
the separated negative may be hardened and softened, it is now immersed in
alcohol containing 5 % of glycerine and 5% of formalin.
The film coming out of this alcoholic glycerine bath is then dried, suitably
pressed on to a scrupulously clean glass plate, varnished, and copied, exactly
like every other negative.
It can, however, be used as an independent film, without transfer to a glass
plate.
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
Improved compound material for photographic negatives, having the sensitive
film separated from the paper base by an interposed layer of resin varnish
rendered flexible by the addition thereto of oils, vegetable glue, gluten or the
like, substantially as described.
Tth 10t
1900
W. P. THOMPSON & Co.,
322, High Holborn, London, W.C., Patent Agents for the Applicant.