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Document number: 9632
Date: 25 Mar 1845
Recipient: TALBOT William Henry Fox
Author: WOODS Thomas
Collection: PUBLISHED
Last updated: 23rd June 2014

[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. 97-98.]

March 25, 1845.


I am sorry I did not receive you letter before Dr. Robinson left this town, which I should have done, it being dated March 18: I did not get it until March 24. I will, however, forward it to him, am I am sure he will, with his usual kindness, make whatever use of it he thinks right. I will ask him to have it laid before the Academy with my Paper. I agree with the observations you make on my Paper on general principles. There is no doubt at all that your Calotype, Mr. Hunt's Energiatype,<1>, and my Catalysotype<2>, if I may be allowed, for the present, to call it so, are all pretty similar in their modes of action, and perhaps they all come to the same point in the end, - the decomposition of the salt of silver; but, as I said in my former letter, if new modes of producing this effect were not be named, why call your process Calotype - why call Mr. Hunt's Engergiatype, &c., as they all agree in their general results with the first experiments made with light on the nitrate of silver? Why not regard them all merely as instances of the same general principle, and not isolate them, as it were, by designating each by a particular name? You will say now that I agree with your ideas: I always did. I think that cumbering science with a multiplicity of hard names for every particular fact is very bad; but the christening of my process has been forced on me by a similar line of conduct in others; and when a nomenclature sufficiently good appears (a task which I wish you would undertake), I will be the first to blot out the word Catalysotype.

I do not pretend to any discovery; nor do I think my process, in its chemical character, distinct from the general mass of facts in active chemistry. I merely regard it as a new combination, acting with great facility, very little complication, and, though not involving a new principle, being developed without requiring any second wash, which I looked on as characteristic until you mentioned the io-gallic paper, a process of which I was certainly ignorant before. You mention also Mr. Hunt's Energiatype as being similar to mine; but, as first published, it undoubtedly could have no claim to the advantages mine possesses, either in facility of execution or rapidity of result. I think he says it requires six or eight minutes to accomplish what mine does in two or three seconds. After my process was published by being read at the meeting of the Association at York, the sulphate of iron was applied to iodised paper, but not before. That proceeding has increased its sensibility, and made it approach in sensibility to mine; but it obviously does not interfere with my right to consider the Catalysotype my own child, and to call it what I please. However, I think all experimentors with light owe you a great debt, and should pay particular attention and respect to your opinion on a subject for which you have done so much; I will, therefore, not insist on adhering to the word Catalysotype, but leave the process to be dealt with as a fact in the general history of active chemistry. For the present the name must be borne with, as my Paper is written and given to Dr. Robinson; but if it ever should be again spoken of, which is perhaps not improbable, we will not elevate it to the honour of a distinct prefix.

I am, &c.
Thomas Woods.


1. Hunt, "Energiatype: A New Photographic Process," Athenaeum, no. 866, 1 June 1844, pp. 500-501. In September, Hunt elaborated on this process at the BAAS meeting, chaning its name: "On the Ferrotype, and the Property of Sulphate of Iron in developing Photographic Images." Talbot responded to Hunt's presentation, outlining his own experiments with iron, pointing out that the spontaneous development was in fact how he first discovered the calotype process, and feeling that Woods' process was only a variation on the calotype. Report of the British Association for the Advancement of Science, 1844, pt. 2, pp. 36 and 105.

2.Woods' chosen name of catalysotype derived from his feeling that the process depended on a catalytic action (one in which a substance changes the speed of a chemical reaction - in this case accelerating it - without itself being consumed in the process) to develop the image. Woods used a syrup of ioduret of iron mixed with a solution of silver nitrate. After exposure in the camera, the image developed spontaneously and then only needed to be fixed, either with potassium bromide or potassium iodide.

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