[The original has not been located. This was published as a letter to the editor in the Athenĉum, no. 1262, 3 January 1852, p. 23.]
[A portion "not sent" is Doc no 06544].
Dr. Woods has communicated to me a copy of a letter which he has written to you concerning my new photographic process. This courteous proceeding on his part demands my acknowledgment. I think it might with advantage be generally adopted, as tending both to save time and to remove misapprehensions. I am a friend to free discussion; and therefore can have no objection to the publication of Dr.Woods's letter (although it is founded on a complete mistake). I only request that if you should think fit to publish it, you will accompany it with this reply.
In my paper which appeared in the Athenĉum of Dec. 6, I took particular pains to attribute to Dr. Woods the merit, which I consider a great one, of having first introduced the use of iodide of iron in photography. Its component parts, iodine and iron, were already in extensive use among photographers, but they had not been used in combination until that was proposed by Dr. Woods. With this exception - namely, the employment of iodide of iron - there is not the slightest resemblance between the process which I have called Amphitype and that which Dr. Woods has denominated Catalysotype. My pictures are formed upon glass, -those of Dr. Woods are upon paper. My pictures exhibit both a positive and a negative image, not (as Dr. Woods erroneously states in his letter to you) at opposite sides of the plates, but both on the same side,- the one appearing when the other disappears, according to the direction in which the light shines upon the glass surface. But the pictures mentioned by Dr. Woods as appearing both positive and negative are of a wholly different nature. They are formed upon paper,- the positive image appearing on one side of the paper, the negative on the other. They have nothing to do with the employment of iodide of iron, as they occur frequently in the common process of photography on paper. In order clearly to explain their nature, I will suppose that a Calotype negative is made, and that after fixing it, it is washed on the back with nitrate of silver, and then exposed in a copying frame with its front surface turned towards the light. Then, it is evident that a positive copy of the picture will be gradually formed upon the back of the paper, and may be afterwards fixed in the usual way. Now, the process which I have here supposed to be purposely executed, sometimes occurs spontaneously, but always in that case much more imperfectly. Indeed, I have never seen a producible positive picture formed in this way,- and I have therefore always regarded it as a mere scientific curiosity. I held, however, no idea that Dr. Woods claimed to have discovered it. I have myself known it these ten or eleven years; but if it was really first published by Dr. Woods, he ought to have the credit of it, according to the usual rule. At any rate, it has nothing whatever to do with the process which I have called Amphitype, and described recently in the pages of the Athenĉum. There are no two processes in Photography more dissimilar. Upon grounds of equal justice my new process might have been claimed by the friends of Daguerre as a mere variation of the Daguerreotype; because, in fact, if a Daguerreotype picture is held in a certain, light it changes from positive to negative. And, indeed, my Amphitype process bears an infinitely, greater resemblance to the Daguerreotype than it does to the pictures produced upon paper, which are positive on one side and negative on the other. With respect to my introduction of a new name, such as Amphitype, I justify it on the ground of convenience. There are ten or twelve photographic processes, so different that they require distinctive names,- such as Cyanotype, Chrysotype, &c.,- if we would avoid the use of very inconvenient periphrases. Whoever proposes a new name does so at his own risk. If it is found not to be required, it, is sure soon to be forgotten. My definition of "Amphitype" is "a photographic picture, upon glass, appearing alternately positive and negative, according, to the direction of the light in which it is held:"- and it comprises at present two varieties,- viz., the process as described by me in the Athenĉum, and the Collodion process. If Dr. Woods will give an equally brief and clear definition of his Catalysotype, it will then be for photographers to say whether it ought to take rank as a separate genus or species of photography, or whether it should only be classed as a modification. I informed Dr. Woods in 1845 that I thought it only differed from my Calotype process in the use of iodide of iron as an accelerative agent in the production of the negative, the finally resulting or positive copies being identical:- but, of course, I can have no objection to a contrary opinion being expressed by those who may entertain it. I only affirm that the question is now brought forward without necessity; there not being the slightest resemblance in the results obtained by my new process and by that described by Dr. Woods in 1845 as applicable to paper.-
I am, &c.