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Document number: 9599
Date: 18 Mar 1845
Recipient: WOODS Thomas
Author: TALBOT William Henry Fox
Collection: PUBLISHED
Last updated: 9th August 2010

[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. 95-97.]<1>

Lacock Abbey, Chippenham
18th March, 1845


I have to acknowledge the receipt of your courteous letter of the 15th instant, upon which I beg leave to make a few observations. In my Calotype process, iodide of silver is decomposed by the joint influence of light and a deoxydising agent (gallic acid). Mr. Hunt has shewn that sulphate of iron may be substituted for gallic acid, and he calls the process so altered Energiatype.<2> But since tannin and other substances may also be substituted for gallic acid, each of these variations in the process would require, on the same principle, to have a separate name, which would, surely, be inconvenient. In your method, iodide of silver is decomposed by the joint action of light and iron; the three reacting substances being the same as in Mr. Hunt's Energiatype; and therefore, imperfect as the theories of photography confessedly are, I cannot persuade myself that a catalytic action can take place in your process, unless it also takes place in the Energiatype and in my original Calotype process: I therefore cannot help but considering these three processes as variations of the same, and not essentially different. I hope, however, you will not consider me as detracting in the least from your valuable labours: my remarks refer only to the nomenclature of the science.

If I am not mistaken, the three methods I have named produce pretty nearly identical results, though I speak from the experience of only two of them, Mr. Hunt's and my own. Both of these are nearly certain in operation, very rapid, giving a camera picture of a bright object in a second of time, and requiring no second wash if enough of the deoxydising agent is employed in the first wash. It is customary to make the positive copies on a different paper, which I have called photogenic drawing-paper, consequently, the final results of the two processes cannot anyhow be distinguished.

I thank you for your courtesy in mentioning that you are about to send a Paper on the subject to the Royal Irish Academy by the hands of Dr. Robinson. May I request that this letter and my former one, with permission of the Academy, may be read to them on the same occasion, if Dr. Robinson will kindly take charge of them. It may be left to their scientific judgment to say whether a new principle is involved or not in your experiments. If any new principle be involved, then a distinctive name, such as you have given, is, of course, desirable, - otherwise it would not be so. I would refer also to the instance of the Daguerreotype, now so differently managed from what it used to be at the time of its first promulgation. It is now at least a hundred times more rapid in its effects, but it still continues to be called the Daguerreotype. On the other hand, I believe it is not affirmed that any process on paper has been discovered more rapid or more certain than the Calotype; I am not aware of any such having been as yet described. We should certainly be very grateful to any one who discovered a more rapid process, depending on new combinations; but if I do not err in defining the Calotype process as depending on a combination of iodine, silver, and a deoxydising agent, your process would be included in that definition, unless good reasons to the contrary could be shewn, all which I willingly leave to the judgment of the scientific world: and, thanking you for your polite attention in so soon answering my last letter,

I remain, Sir, Your's very truly,
H. Fox Talbot.

P.S. - If your process does anything which the Calotype cannot do, or does it better, I willingly admit its importance; but I apprehend that you are not aware of the facility and rapidity with which our Calotype operations are now conducted. Indeed, that was my chief reason for troubling you with a letter, as your Paper read at the York meeting mentioned the spontaneous development of photogenic images as something new, whereas it is a phenomenon of very frequent occurence in the Calotype, and always occurs when we use the io-gallic paper.


1.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.

2. Hunt, "Energiatype: A New Photographic Process," Athenĉum, no. 866, 1 June 1844, pp. 500-501. In September, Hunt elaborated on this process at the BAAS meeting, changing 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.

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