Improvements relating to Photographic Printing.
Year: 1899

page_text: [Communicated from abroad by REDFIELD BENJAMIN WEST, of Guilford, County
of New Haven, State of Connecticut, United States of America, Physician.]
Improvements relating to Photographic Printing.
I, HENRY HARRIS LAKE, of the Firm of Haseltine, Lake & Co., Patent Agents,
45, Southampton Buildings, in the County of Middlesex, do hereby declare
the nature of this invention and in what manner the same is to be per-
formed, to be particularly described and ascertained in and by the following
statement:-
-:
This invention relates to an improvement in sensitizing paper for photographic
printing, the object of the invention being to produce a composition for sensitiz-
ing paper which may be readily compounded, which is quick in action, easy to
prepare, inexpensive, and from which prints may be produced having the
appearance of those made on platinum paper, with the advantage over the latter
that the paper is blackened by light, and so that the printing can be watched
as it proceeds without timing it, and whereby the prints may be made in less
time and with the exercise of less skill, and the invention consists in sensitizing
paper with the composition hereinafter described and particularly recited in the
claim.
The paper employed may be of the usual character, and the sensitizing com-
pound consists of ammonium nitro-prusside 25 parts, ammonio citrate of iron,
or as it is sometimes called a double citrate of iron and ammonia, 30 parts, and
water 100 parts. To this may be added small quantities of other citrates for the
purpose of modifying the color of the prints. For example, the citrate of
magnesium to produce an engraving black, or the citrate of zinc for a brown.
These while not absolutely necessary for the success of the sensitizing paper, are
of use for producing certain tints. Other soluble nitro-prussides such as sodium
nitro-prusside or potassium nitro-prusside can be substituted for the ammonium
nitro-prusside, but they are not as sensitive to light as is the ammonium nitro-
prusside, which is therefore to be preferred. Paper coated with this sensitizing
compound is sensitive to light, by exposure to which it becomes brown or black,
so that when exposed to light under a negative in the usual manner for printing
photographs, a picture in light and shadow is produced on the paper. This
print is then washed in water for two or three minutes to remove superfluous
chemicals, and then subjected for five minutes to a bath containing a mordant
like acetate of lead in 2% aqueous solution, for the purpose of rendering the
print permanent. For this bath any other well known bath for fixing the print
may be employed. No further manipulation is necessary except a slight washing
of the print in water.
The proportions given in the foregoing formula have been found in practice
to give good results, but they may be varied to some extent without materially
changing the result. I do not, therefore, wish to be limited to the precise
proportions named.

page_text: Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed, as communicated to
me by my foreign correspondent, I declare that what I claim is:-
1. The herein described composition for sensitizing paper, consisting of a
soluble nitro-prusside, ammonio citrate of iron, and water, in the proportions
substantially as described.
2. The process of developing photographic prints, consisting in subjecting a
print made on paper sensitized with a composition composed of soluble nitro-
prusside, ammonio citrate of iron, and water, to a bath containing acetate
of lead.
Dated this 23rd day of May 1899
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, W.C.,
Agents for the Applicant.