William Willis Patent 1887 #1681
Improvements relating to Photo-chemical Printing
British Patent #1681, 2nd February 1887, William Willis Jnr
Specification
My invention has for its object the production, upon paper or other surfaces, of photographic pictures or images in platinum, that is to say, pictures of images of which the colouring matter or pigment is platinum. It differs from the processes of photo-chemical printing described in the specifications of my former patents, viz. :— No. 2011 dated 5th June 1873, No. 2800 dated July 12th 1878, and No. 1117 dated March 15th 1880, in which processes (as far as they relate to platinum) the paper or other surface is coated with a solution of a salt of platinum and sometimes other salts and also with a solution of ferric oxalate. The solutions are applied, either separately or mixed, to the paper, and in all cases the sensitive coating of the paper contains a salt of platinum and ferric oxalate. After exposure to light, the prepared surfaces are treated with one or other of the developing solutions described in the said Specifications.
Hitherto no means have been known by which the salt of platinum could be employed entirely in the developer or developing solution, instead of wholly or partly in the sensitive coating of the paper or other surfaces as above set forth. I have, however, now discovered a process by which I can accomplish this result. For this purpose I apply to paper or other suitable material which has been rendered sensitive by a coating of ferric oxalate and afterwards exposed to light, a developer containing salts of platinum and certain soluble phosphates (or other salts, in which the ferrous oxalate image produced by exposure to light is insoluble or nearly so), with or without the addition of potassic oxalate, potassic tartrate, ammonic citrate or other salts which tend to increase the rapidity and vigour of the development. By this process I avoid the necessity of using salts of platinum in the sensitive coating of the paper or other surfaces. I thereby greatly diminish the cost of the process and can gain good results without heating the developer.
Moreover I obtain a slower developing action so that it is possible to watch the progress of development and to arrest it at any desired moment by washing the print in a solution of acid.
According to my present invention I use paper, wood, woven fabric or other material the surface of which I prepare and render sensitive for photographic purposes by the application of a coating or coatings containing ferric oxalate with (or without) the addition of a salt of lead or of mercury, or mixtures thereof, and without any salt of platinum.
I first prepare the paper or other surface by the use of this coating as hereinafter specified. I then expose it to light under or behind a negative and then develop the picture by means of one of my improved developing solutions hereinafter specified, or other suitable solution containing a salt of platinum.
For preparing or coating the paper or other material, I employ for ordinary purposes an aqueous solution of ferric oxalate containing in each fluid ounce about sixty (60) grains of ferric oxalate Fe2(C2O4)3 ; but I may use less or more of the latter according to the result desired to be obtained. I am of course aware that there are other salts of iron sensitive to light, but the oxalate is the best for my purpose. I sometimes mix or dissolve in the ferric oxalate a salt of mercury or of lead or of a mixture of these salts ; for instance, I dissolve in fluid ounce of the ferric oxalate solution above described, from [IL: missing] grain to three grains of mercuric chloride. Or I apply a solution of a salt of lead or mercury or a mixture of these salts to the paper or other surface either previously or subsequently to coating the same with ferric oxalate. I find the mercuric salt very useful where a warm tone or effect somewhat resembling sepia is desired.
I do not confine myself to aqueous solutions of the above salts.
The paper thus coated, after being dried, is ready for use. If two coatings are applied to the paper or other surface ; it should be dried between the application of the first and second coatings. After its exposure to light under or behind a negative, I apply it to the developing solution.
I prepare an improved developing solution or developer as follows, that is to say :— I use solutions of various soluble phosphates. I have been most successful with the following, viz. :— the monosodic or disodic, the monopotassic or dipotassic or the mono-ammonic or diammonic orthophosphates, or mixtures or combinations of these salts with one another, and with or without the addition of other salts such as potassic oxalate, ammonic citrate and others. In all cases I add to these solutions or mixtures of solutions a salt of platinum. I mix a solution of this salt with the above named solutions or I dissolve the platinum salt in them. The platinous salts most suitable for my purpose are the ammonic, potassic and sodic chloro-patinites, the ammonic, potassic and sodic bromo-patinites or mixtures of them, and in some cases I use a very small quantity of a platonic salt, such as ammonic, potassic or sodic chloro-platinate.
I usually prepare this solution as follows, that is to say :— I dissolve in one fluid ounce of water, one hundred (100) grains of di-potassic orthophosphate, forty (40) grains of potassic oxalate and ten (10) grains of potassic chloro-platinite ; or I may make it in another manner, viz. : by dissolving in one fluid ounce of water, one hundred (100) grains of diammonic orthophosphate, thirty five (35) grains of ammonic citrate and ten (10) grains of ammonic chloro-platinite ; or I make similar developing solutions with the salts previously mentioned. I make also developers containing only phosphates and salts of platinum, that is to say, I may make a developer by dissolving in one ounce of water, about one hundred (100) grains of mono-potassic or di-potassic orthophosphate or mixtures of these salts and ten (10) grains of potassic chloro-platinite.
The developing solution is applied to the paper or other surface (after the same has been exposed to light) by pouring it over the same, or by immersing the paper therein, or by floating the paper thereon, or by means of a brush or otherwise. It is applied cold, warm or hot as desired. A cold solution usually takes longer to effect the development of the picture than a hot one. The strength of the solution may be varied ; usually the best results are obtained by strong solutions of the phosphates and other salts ; the platinum salt will ordinarily be used in the proportion of from five to ten grains of the salt to one fluid ounce of the developer.
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 claim—
First. The process or method in which I sensitize the surface of the paper or other material by the means herein specified, then expose the surface to light and then develop the picture or image by the use of a solution containing a salt of platinum, as above set forth.
Second. The production or development of photographic pictures or images in platinum by the application of a salt of this metal to a surface which has been previously rendered sensitive by the application of a ferric salt and exposed to light.
Third. Paper or other material which has its surface prepared and rendered sensitive for photographic purposes by the application of a ferric salt and a salt or mercury or of lead or of both mercury and lead as above set forth.