William Willis Patent 1887 #16003
Improvements relating to Photo-chemical Printing
British Patent #16,003, 21st November 1887, William Willis Jnr
Specification
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 AD 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 pictures, that is to say, although the shadows will be of a pure black tone, there will sometimes be a slight trace of brown in the high lights of the developed picture. This is a defect which does not impair the value of the 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 generally 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 or 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 throughout, 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 of lead with the image at the time of its development, I obtain a better reducing action and avoid the necessity of using in the developing solution phosphates or other salts for rendering the ferrous image insoluble, the presence of such 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.
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 a mixture of these, or together with other substances which aid in the reduction of the metal from the salt or [IL: of] platinum by the ferrous image produce as aforesaid.
Or I adopt the following method, viz. ;— 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 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 the mercuric chloride. The ferric oxalate and the lead or mercuric salt can be applied together in one solution, or the said salts can 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 surfacee 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 Fe2(C3O4)3 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 pply it to 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 AD 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 hereinabove 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 axalate 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, 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 substance, 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 chloroplatinites, the ammonic potassic and sodi bromo-platinites, or mixtures thereof ; but in some insrtances I use a small quantity of a platinic salt such as 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 to be 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 method or 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 leadf 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 the 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.