Improvements in or relating to the "Dusting-on" Process of Producing Pictures by Photography.
Year: 1890

page_text: Date of Application, 22nd Aug., 1890-Accepted, 11th Oct., 1890
COMPLETE SPECIFICATION.
Improvements in or relating to the "Dusting-on" Process of
Producing Pictures by Photography.
I, GEORGE WILLIAM WOOD of 3 Askew Road, Gateshead on Tyne in the County
of Durham, Clerk 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 :--
دو
My invention refers to improvements in or relating to the "dusting on process of
producing pictures by photography.
In the production of positive pictures by what in photography is known as the
"dusting on" process the support which is generally a plate of glass or opal glass is
coated with a deliquescent organic matter intermixed with bichromate of potassium or
ammonium.
These mixtures are sometimes termed "photogenes" and as such will hereinafter be
referred to.
After drying the support is placed under a diapositive and exposed to the action of
daylight and after exposure the image is developed by dusting on some suitable black
or dark colored matter in the shape of a fine powder the result being a reproduction
of the image of the diapositive employed.
It will thus be seen that if it be desired by this process to make a positive from any
given negative it is necessary in the first place to make by some other process a
diapositive or transparent positive from it (the negative).
The object of my invention is to provide a "dusting on" method or process for
producing positive images or pictures direct from the negative and I effect this as
follows
A support, generally a sheet or plate of any suitable black or dark colored material
such as ebonite or vulcanite or ferrotype plate or glass coated with black or dark
colored varnish or enamel is after being well cleansed coated with a "photogene"
such as the following
Gum Arabic -
30 Grains
White Loaf Sugar
30 Grains
Ammonium Bichromate
Distilled Water
-
20 Grains
-
1 Ounce
This formula works very well although any of the other well known "photogenes"
will answer the same purpose.
After drying the support is placed under a negative and exposed to daylight for a
time dependent on the density of the negative and the strength of the light
generally from 5 to 20 minutes but an actinometer should be used as in carbon
printing.
"
"
The image is next developed by dusting on some suitable lustrous substance
such as the white, gold or other light colored bronze powders obtainable commercially
or aluminium, magnesium, zinc, tin, silver or other suitable metal or alloy reduced to
powder may be used.
It is obvious also that any suitable light colored or white or nearly white substance

page_text: The standard developer employed in the "ferrotype" or collodion positive process
answers well.
The precipitate after being well washed is dried, passed through a fine lawn sieve
and may then be used as above set forth.
"
After "dusting on is complete the plate or support is coated as usual with
collodion well washed and finally varnished as a protection against oxidation or other
injury.
The above procedure may if desired be varied by taking as the support a sheet of
plain glass or other transparent medium, coating with photogene, drying, exposing,
developing and finally “backing up" the support with black varnish or printers ink
on paper as in the collodion positive process on glass.
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 :
"
1. The use of a light colored or white or nearly white substance for "dusting on
a dark colored or black or nearly black support prepared and applied in the manner
and for the purposes substantially as herein described.
2. The improved process of producing positive images or pictures direct from the
negative substantially as and for the purposes herein described.
Tin 20th day of An1900
0
A. CRAWHALL CHAPMAN,
3, St. Nicholas' Buildings, Newcastle-on-Tyne,
Patent Agent for Applicant.