[The original has not been located. This is from the version published in The Photographic News, v. 21 no. 968, 23 March 1877, p. 142.]
4, Circus, Bath
Feb. 15th. 1874.<1>
Dear Sir,
I will send you to-morrow three specimens of my engraving. This art was discovered in 1852 and published in 1853. The great difficulty at first was to obtain the semi-tints. It was found easy to copy letterpress engravings or anything merely black and white; but graduated shading offered a difficulty.
The main fact upon which the art reposes is the photographic quality of bichromate of potash when mixed with gelatine, discovered by me in 1852, concerning which, as it was a great step in photography, allow me to say a few words.
Mr. Ponton discovered in 1839 that paper became sensitive to light when washed with a solution of this bichromate. No use was made of this knowledge for thirteen years, when, in 1852, I attempted to engrave, and after various other things had been tried, with results more curious than useful, I thought of trying the bichromate mixed with gelatine, which proved successful. I had rather anticipated a failure, because many other photographic substances will not unite with the gelatine, but cause it to curdle. I have always considered this process to be one of the most useful things I have done in photography. I sent a great many specimens to Monsieur Biot, which were given away by him at a meeting of the French Academy of Sciences in April 1853. Several writers on photography have fallen into error, and attributed the discovery to a Frenchman, who published it anew, I believe, two or three years later.
Believe me, yours very truly
H. Fox Talbot<2>
[The Editor added: "It is very interesting to note the fact that Mr. Fox Talbot, the actual inventor of silver printing and of the negative process, was the first to give a practical application to Mr. Mungo Ponton's discovery of the photogenic properties of the chrome salts. It would not be fair, however, to overlook the fact that Mons. Becquerel had previously taken up Mr. Ponton's process, and ascertained that the action of light in this method rendered insoluble the gelatine or other sizing matter in the paper sensitized by a salt of chromic acid, and that M. Poitevin was the first who actually employed these reactions in carbon printing."]
Notes:
1. Vernon Heath introduced this publication: "Three years ago, when lecturing at the Royal Institution, I intended to make use of a letter I had received only a day or two before from Mr. Fox Talbot, but I had only time to refer to it in the very slightest way. I had, however, in my lecture last week an opportunity to read two or three passages from it, and I was struck with their historical interest which I believe to be sufficiently great to justify me sending you the following copy: -"
2. Vernon Heath commented: "It is certainly interesting that Mr. Fox Talbot, who holds the rank of pioneer of the photographic processes in this country, should have discovered the process upon which is based nearly the whole of the present methods of permanent printing."