Improvements relating to Photography in Natural Colours.
Year: 1891

page_text: Date of Application, 26th Nov., 1891-Accepted, 23rd Jan., 1892
COMPLETE SPECIFICATION.
Improvements relating to Photography in Natural Colours.
I Dr. RAPHAEL Korr of Munster (Lucerne), in the Republic of Switzerland,
Chemist, do hereby declare the nature of this invention and in what manner the
ame is to be performed, to be particularly described and ascertained in and by the
ollowing statement :-
My invention relates to photography in natural colours, for the purposes of
which employ a paper and baths of special composition, as hereinafter
described.
In carrying my said invention into practice I use the paper called Rives paper,

page_text: volume by evaporation. This very important solution keeps well and must not be
strengthened.
Now I place the blue silver chloride paper for immediate requirements (supplies
cannot be kept for colouring) in the liquid prepared exactly as above stated and
turn it over for half a minute. I let it drain and place it in a 3 per cent. solution of
zinc chloride shaking the vessel until the said paper has again turned blue. The
paper is then well washed in running water. It is pressed between blotting paper
and placed again for six minutes in the mercury bath. On being removed from
this bath and pressed between blotting paper, it is ready to be exposed. The
paper must not be allowed to dry before it is exposed, as the exposure has to take
place in the damp state.
After the exposure which varies according to the light and the season and which
is determined by a little practice, the yellow and green portions will be already well
defined upon the paper, whilst the other colours, including the white, are covered
with a yellow fog. For removing this fog the photograph is put in a developing
bath. However, before this takes place the green and yellow colours, which are
visible upon the photograph and could not withstand the developing bath, must be
covered with a coating of varnish. When this coating is dry the bath cannot
act upon the varnished portions and the colours will be protected at the said
portions.
After each varnishing the layer or coating is heated over a fire in order that the
varnish may spread uniformly. The photograph is not introduced into the
developing bath, which consists of a 2 per cent. solution of sulphuric acid, until
the varnishing of the yellow and green portions and the drying of the varnish has
taken place. The photograph being left in this bath, the vessel is vigorously
shaken and the yellow fog disappears. All the colours including white appear in all
their brilliancy. I wash rapidly in running water and dry between blotting
paper.
For fixing and finishing the image I proceed as follows, that is to say, after the
photograph has been taken from the developing bath and washed it is again put in
the mercury bath for five minutes. I press it and put it again in the developing
bath until the colours including the white appear again. From this moment no
more washing is needed, but simply pressing. Next the photograph is coated with
a solution of gum-arabic containing 5 per cent. of sulphuric acid this solution of
sulphuric acid and gum must be prepared beforehand, because a precipitate is
formed and the solution must be used clear. The photograph coated with this
solution-is dried by heat and finally varnished.
All these manipulations require practice and accuracy. It is necessary to employ
as much as possible only perfectly pure chemical ingredients.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed, I declare that what I
claim is :-
The process and means for producing sensitized paper, with the mode of manipu-
lating the same, in order to obtain a photograph of any object in its natural colours,
substantially as hereinbefore specified.
Dated this 26th day of November 1891.
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, Agents for the Applicant.