Year: 1887

page_text: 1, WILLIAM WILLIS of Bromley, in the County of Kent, Manufacturer, do hereby
declare the nature of this invention and in what manner the same is to performed, to
be particularly described and ascertained in and by the following statement :-
My invention has for its object the production of photographic pictures or images
in platinum, by improved methods of carrying into effect the process described in
the specification of my former Letters Patent dated February 2nd A.D. 1887
No. 1681.
By the said process I have been enabled to produce pictures of excellent quality
and to greatly diminish the cost of the platinotype process and obtain other
important advantages. I have, however, found that I do not in using the
process, as described in the said former specification in all cases, obtain an absolute
uniformity of tone or colour or monochromatic effect in the picture, that is to say,
although the shadows will be of a pure black tone, there will be sometimes a slight
trace of brown in the high lights of the developed picture. This is a defect which
does not impair the value of a photographic print in respect of accuracy and other
qualities, but the presence of two colours may be considered offensive to good taste.
In the picture of a landscape for instance, it is generally conceded that the foreground
shadows should be warmer in tone or colour than the high lights and delicate distance,
or certainly not colder.
Now although I have not succeeded in producing pictures in which the darker parts
or shadows are warmer in tone than the lighter and more delicate portions or high
lights, yet I have as one result of my present invention provided for carrying into
effect the said process with the certainty that the tone or colour shall be uniform through-
out, that is to say, I can be sure that no part shall be of a warmer tint than another
part of the picture.
The process described in the specification of my said patent No. 1681 is distinguished
from former processes of mine chiefly by the fact that the platinum is contained
entirely in the developing solution, that is to say, I described a surface coated with
ferric oxalate (with or without a salt of lead or of mercury and without any platinum)
and the use, for developing the image or picture thereon, of a solution containing a
salt of platinum in all cases mixed or combined with a phosphate or other salt in
which the ferrous image is insoluble, and sometimes with other salts. I now find,
however, that, by ensuring the presence or contact of a salt of mercury or of lead
with the image or picture at the time of its development, I obtain a better reducing
action and avoid the necessity for using in the developing solution phosphates or other
salts for rendering the ferrous image insoluble, the presence of which salts, as far as
I have been able to observe, is the cause of, or is accompanied by the defect in the
tone or colour of the picture.

page_text: I therefore now proceed according to the following method, that is to say, I coat
paper or other material with ferric oxalate together with a salt of mercury or of lead
or both. Then I expose the coated surface to light under or behind a negative or
other suitable screen, and then develop the ferrous image produced by the action of
light, with a solution containing a salt of platinum together with a salt of oxalic or
citric or tartaric acid, or mixtures of these, or together with other substances which
aid in the reduction of the metal from the salt or platinum by the ferrous image
produced as aforesaid.
Or I adopt the following method, viż. ;-I use a surface sensitized by ferric oxalate
alone and then, after exposure to light, develop the picture or image with a developing
bath or solution containing one or more of the above named salts or substances which
aid in the reduction of platinum in the manner aforesaid, together with a salt of
platinum and also a salt of lead or of mercury or both, but in this case preferably the
salt of lead.
It will be observed that the lead or the mercury, one or the other of which is in all
cases essential in the practice of my invention, is in the one case present in the sensitive
coating of the paper before its exposure to light, and in the other case is wholly in the
developer. But for some purposes I use a salt of mercury or of lead both in the
sensitive coating of the paper and in the developer.
In practising my invention according to the first method above described, I coat
the paper or other surface with ferric oxalate (or with a compound or mixture of the
same and other oxalate of an alkali metal) together with a salt of lead or of mercury
or of both. The salts of lead which I find best for my purpose are the nitrate and
chloride. If I use salts of mercury, I employ only the mercuric salts, and of
these I prefer mercuric chloride. The ferric oxalate and the lead or mercury salt can
be applied together in one solution, or the said salts may be applied separately in
solution to the paper or other surface. I usually apply them in one solution. When
they are applied separately, the paper or other surface should be dried between the
coatings.
In some instances, I employ an aqueous solution of ferric oxalate containing in each
fluid ounce about sixty (60) grains of the oxalate Fe, (C, 04), more or less according
to the result desired to be obtained. And I add to, or dissolve in each ounce of this
solution one (1) grain of plumbic chloride and one (1) grain of mercuric chloride.
I sometimes omit the lead salt from this solution and increase the quantity of the
mercuric salt, that is to say, instead of one (1) grain of mercuric chloride I use two
or more grains of this salt.
.
The paper thus coated, after being thoroughly dried, is ready for use. After its
exposure to light under or behind a negative or suitable screen, I apply to it the
developing solution.
I prepare this developing solution with potassic oxalate and potassic chloro-platinite
as described in the specification of my former Letters Patent No. 2800 A.D. 1878.
I prefer to use an aqueous solution of these salts containing in each fluid ounce
about ninety (90) grains of potassic oxalate and nine (9) grains of potassic chloro-
platinite.
Or I use, for developing, an aqueous solution containing in each fluid ounce about
sixty (60) grains of ammonic tartrate and eight (8) grains of ammonic chloro-platinite.
Or I make developing solutions with any of the other salts or substances herein-
above mentioned as applicable for this purpose, or with other salts which tend to aid
in the reduction of the platinum salt by the ferrous image produced by the action
of light. In practising my invention according to the second method hereinbefore
specified, I first apply to the paper or other surface a coating of an aqueous solution
containing about sixty (60) grains of ferric oxalate in each fluid ounce of solution.
I then dry the coated paper and then, after exposing it to light under or behind a
negative, I apply to it the developing solution.
For this developing solution I sometimes employ an aqueous solution containing in
each fluid ounce about ninety (90) grains of potassic oxalate and nine (9) grains of
potassic chloro-platinite. To this solution I add a solution of a salt of lead,

page_text: preferably the acetate, until a permanent precipitate begins to form. If I use a salt
of mercury instead of a salt of lead I prefer the mercuric chloride of which I
dissolve (or add) about five (5) grains in each fluid ounce of the said solution. The
salts of mercury do not in all cases ensure a monochromatic tone in the picture, but
in other respects they afford good results.
Or I use a developing solution containing a salt of platinum and a salt of lead or
of mercury and one or more of the other hereinbefore specified salts of oxalic,
citric and tartaric acids or substances, but when a salt of lead is employed, there
must be no salt used in the developer which would entirely prevent the solution of
the lead salt. These developing solutions containing lead or mercury salts or both
can also be used for developing photographic pictures or images on paper and other
surfaces which have been coated with ferric oxalate together with a salt of lead or of
mercury.
I sometimes apply the constituents of the developer separately or in two solutions
to the sensitive surface after it has been exposed to light. In this modification of
my process, I first apply a solution of plumbic acetate or of mercuric chloride to the
said surface and then quickly, without washing or drying the surface, apply to it
in solution the remaining constituents or ingredients of the developer.
The developing solutions mentioned in this specification I prefer to apply cold, but
occasionally I apply in a heated state such of them as are not decomposed by heat.
The salts of platinum which I prefer to make use of in the developers herein
described are the platinous salts viz. the ammonic, potassic and sodic chloro-
platinites, the ammonic potassic and sodic bromo-platinites, or mixtures thereof; but
in some instances I use a small quantity of a platinic salt such as the ammonic,
potassic or sodic chloro-platinate. The coating and developing solutions are applied
as described in my former specifications or by other suitable means.
Having now particularly described and ascertained the nature of my said invention,
and in what manner the same is to be performed I wish it understood that I do not
limit myself to the proportions above stated nor do I limit myself to the use of
aqueous solutions for the purposes of forming the coating or sensitizing and
developing solutions as I may use any suitable solvent for the salts employed in my
process, and I claim :-
First The mothe process of photo-chemical printing wherein I modify or
vary the process described in the specification of my said Patent No. 1681 by
ensuring the presence or contact of a salt of lead or of mercury with the image
during the development and by avoiding the use of phosphates, or other salt in
which the ferrous image is insoluble, as, and for the purpose, herein set forth.
Second. The development of a photographic picture or image by a solution (which
contains a salt of platinum and which does not contain any phosphate) applied to a
surface sensitized by the application of a solution containing ferric oxalate and a salt
of lead or of mercury or both, as above set forth.
Third. The development of a photographic picture or image by a solution (which
contains a salt of platinum together with a salt of lead or of mercury and which
does not contain a phosphate) applied to a surface that has been sensitized by a
solution containing ferric oxalate with or without a salt of lead or of mercury, as
above set forth.