[The original has not been located. The letter was read at a meeting of the Royal Irish Academy in conjunction with a paper by Dr. Thomas Woods on his Catalysotype and published in the Proceedings of the Royal Irish Academy, v. 3 no. 50, 12 May 1845, pp. 94-95.]
Lacock Abbey, Chippenham
11th March, 1845
Excuse my addressing you on the subject of a Paper which you sent to the British Association at York, last September, containing the description of a photographic process.
Some years ago I described a process for obtaining camera pictures without using any second wash. It was described nearly as follows in the specification of my English patent: take iodised paper, wash it with gallic acid, dry it, and keep it in store for subsequent use. This is called io-gallic paper from its constituents. When wanted, take a sheet of io-gallic paper, wash it with nitrate of silver, and put it in the camera. The image obtained is generally, at first, invisible, but it rapidly developes itself when remove from the camera, requiring no further care, except ultimately to fix it. Instead of gallic acid, sulphate of iron answers the same purpose perfectly. The same effect is very often, but not always, produced in the ordinary Calotype process, which I described in 1841; indeed I discovered it that way.
The process which you have called Electrolysotype <1>appears to me to be strictly analogous to the above. If I comprehend your description, you use an iodised paper in which iodide of iron is employed instead of iodide of potassium.
You may be quite right in attributing the effects to Electrolysis, but then it follows that my Calotype process, with all its variations, must result from the same cause.
I am, Sir, Your obedient Servant,
H. Fox Talbot.
1. Dr. Thomas Woods, "On the Electrolysotype; a new Photographic Process," Report of the British Association for the Advancement of Science, 1844, section two, pp. 36-37. Woods used a sugar syrup solution of ferric iodide and a solution of silver nitrate to make a negative paper, one he felt was sufficiently sensitive to take portraits in the shade in fifteen seconds, and a picture of moonlight in fifteen minutes. The exposed negative would develop spontaneously in the dark, a process he ascribed to electrolysis.