William Willis Patent 1878 #2800

Willis’ Improved Process of Photo-chemical Printing

British Patent #2800, 12th July 1878, William Willis Jnr

Specification

This invention is based upon the process described in the Specification of my former Letters of Patent, dated June 5th, AD 1873, No. 2011, which process consists in the production on suitable surfaces, such as paper, wood, silk, prepared canvas, and others, of photographic pictures in platinum, iridium, or other metal by the application of solutions of potassic or ammonic oxalate to such surfaces after they have been exposed to light or insolated under or behind a negative or other object, and which surfaces have been coated previously to such insolation with ferric and other salts, one of which is a salt of the metal in which the picture is to be produced.

But although good results are produced by the process above set forth, I have discovered means whereby I obtain greatly superior results in photo-chemical printing and produce pictures or images characterized by great permanence, and am enabled to effect such printing in a more simple and certain manner, and with greater uniformity in the results than heretofore ;  and these improved means form the subject of my present invention.

The said Invention consists in an improved process of photo-chemical printing, whose essential feature is the addition of a salt of platinum, or of iridium, or of mercury to the solution of potassic or ammonic oxalate used as described in the former Specification, and which improved process is as follows, that is to say :— The application to paper or other surfaces of a solution consisting of potassic or ammonic oxalate mixed with a salt of platinum, of iridium, or of mercury after such paper or other surface has been exposed to light under or behind a negative or other object, and which paper or surface has previously to such exposure to light received a coating of or has been treated with ferric oxalate and with other salts, one of which is a salt of the metal in which the picture or image is to be produced on the said paper or other surface.

According to the said Invention I proceed as follows, that is to say :— If paper is used I coat the same with an aqueous solution which I term the coating solution, and which must contain as one of its ingredients a salt of the metal in which the picture or image is to be produced.  For instance, when I desire to produce the picture in metallic platinum each fluid ounce of this solution will contain about 15 grains of potassic chloro-platinite, 70 grains of ferric oxalate (with enough oxalic acid to render this ferric oxalate freely soluble), and preferably two grains of plumbic chloride.  I then dry the paper and expose it to light under or behind the negative or other object from which the picture or image is to be produced on the prepared paper for a sufficient time, which will usually be indicated by the image or picture becoming faintly visible.  I then float the said paper with its face or coated surface downwards on or immerse it in an aqueous solution, preferably hot, which I term the developing solution, and whose use in the process constitutes the novel and essential feature of my Invention.  Each fluid ounce of this developing solution contains 120 grains of potassic oxalate and 7 grains of potassic chloro-platinite, or other salt of the kind herein-after specified.  This solution quickly deepens in color or blackens the picture or image produced on the coated paper by the action of light.  I then wash the paper in a weak solution of some acid (preferably oxalic acid), and finish by washing it in plain water.

The coating solution or solutions for treating the paper or other surface previous to its insolation or exposure to light constitutes no part of my Invention irrespective of the subsequent treatment of the coated surfaces by the developing solution ; and I may use other salts of platinum in this coating solution, or salts of other metals than those named above, such as salts of gold, iridium, or of palladium ;  but it is essential in all cases that ferric oxalate should form one of the ingredients or constituents of the coating or coatings applied to the said surfaces.

The following are examples of the manner in which I vary the composition of the said coating solution or solutions :—

I sometimes substitute 15 grains of iridium chloride for the potassic chloro-platinite used as specified ;  or I substitute for the two grains of plumbic chloride 4 grains of mercuric chloride.  In other cases I omit the plumbic chloride in the coating compound or solution.

Instead of effecting the coating of the paper or other surface with the aforesaid salts by using the same all in one solution, I may in some instances find it desirable to apply such salts in different successive solutions, and dry the paper, if necessary, between the successive coatings.

I do not confine myself to the use of potassic chloro-platinite as an addition to the aforesaid developing solution, that is to say the potassic oxalate, which I apply to the insolated surfaces, but may use other salts of platinum or salts of iridium or mercury, such as platonic chloride, potassic chloro-platinate, or sodic, ammonic, or baric chloro-platinite, iridic chloride, or mercuric chloride.  But although these and other salts of the above named metals (namely, platinum, iridium, and mercury) when added to or mixed with the potassic oxalate will producegood results, I prefer to employ the potassic chloro-platinite for the purpose of my Invention as set forth.

Nor do I intend to confine myself to the use of acqueous solutions of the chemicals herein-before referred to, as the salts may be dissolved and used with any suitable solvent.

Neither do I restrict myself to the exact proportions of the chemicals used in the above-described process, as above stated, as these proportions may be varied within certain limits, according to the results desired to be obtained or other conditions.

In the final treatment of the paper or other material I do not confine myself to the use of acids, but may employ a solution of any other suitable substance capable of dissolving out the salts or chemicals which may be left in the paper.