[The original has not been located. This is from the printed letter to the editor of The British Journal of Photography, v. 11, 9 December 1864, pp. 494-495.]
ON PHOTOGRAPHY WITHOUT THE USE OF SILVER.
Like others I have been disappointed to find that the Wothlytype <1> process produces an image consisting mainly of silver, for the first accounts of it were calculated to give a contrary impression. Nevertheless I believe it to be a valuable contribution to science.
As the subject of printing without the use of silver occupies at present considerable attention, allow me to say a few words respecting a process recently mentioned by The Times. [see page 500.] Whether it has been noticed in your valuable Journal I do not know, not having seen your last publication.
This process, or at any rate one somewhat similar, and employing like it, the chromate of copper, is very well known to me, as I have practised it for some time. I can strongly recommend it for further examination on account of its extreme simplicity, but, above all, on account of the perfect fixation which is readily obtainable. I am not prepared to say that the prints can be made quite equal in delicacy and beauty of colour to those obtained by the usual silver process; but I feel pretty confident that they are permanent, having exposed them to prolonged action of sunshine without change. I cannot think that they will fade, because I have observed that time produces a darkening of the shades; and, capricious as we know photographic actions to be, yet I cannot think that this darkening is destined to be followed by a contrary action hereafter. Moreover, we know that some photographic processes are permanent; for instance, the cyanotype of Sir J. Herschel, by which process a lady, some years ago, photographed the entire series of British sea-weeds, and most kindly and liberally distributed the copies to persons interested in botany and photography. The whole of these prints remain unaltered after the lapse of several years.
I have found it necessary to give names to the various processes which I have from time to time employed, in order to avoid circumlocution and the chance of error in making reference to them. The process of which I am now treating is called in my memoranda the Polytype, from the fact that it yields so many prints in a short time; but as this is merely a MS. name, if you see any objection to it, or prefer another name, I attach no importance to it.
The process is performed as follows:- Take good white paper and size it well with gelatine; then make a saturated solution of nitrate of copper in water. Mix them in the proportion of two parts of the bichromate to one part of the nitrate. Wash the paper on one side with this solution, and dry it at the fire; but take care not to hold it too near the fire, for that causes the formation of an insoluble brown substance. It is not necessary while drying it to exclude the daylight, but, of course, avoid all unnecessary exposure. The paper when dried is yellow. Expose it to light under a negative for the same time or rather longer than you would if using the common silver process. When taken out of the frame there should be a rather strong image upon it.
The account in The Times then says:- "The print is then floated on a concoction of campeachy wood." Here there is a considerable omission; or, if not, the process spoken of by The Times must depend upon quite different principles from that which I have pursued. My mode of procedure is the following:- Having taken the print out of the frame wash it first with cold water, then in tepid water, brushing the surface with soft cotton wool till you are satisfied that none of the chromate of copper remains in the parts which are destined to remain white. This is sometimes not to be accomplished without the aid of warmer water, or at any rate an immersion of some minutes, or a quarter of an hour. But this is to be deprecated and avoided as much as possible, because it to some extent washes out the dark shades caused by the action of light; and if these do not remain tolerably dark after the paper is washed and dried, the resulting print will be feeble. The next thing to be done when the print is dry, is to wash it over with a strong solution of prussiate of potash in order to give it a richer tint. It is immaterial, however, which is used first - the prussiate or the pyrogallic acid. Indeed they may be mixed together, for they do not react upon each other. The development is soon effected, and the print assumes a deep bistre colour (of various shades) which in the course of a month or two I have sometimes found to deepen into black. The print is then dipped into two or three vessels of warm water successively to wash out the pyrogallic acid. This part of the process requires particular attention: for, if the smallest particle of free pyrogallic acid be left, it in the course of time undergoes decomposition, and is resolved into carbon, which becomes visible upon the paper, and gives it a dirty appearance, which, if it exists even in a trifling degree, injures the print very much. But the washing required to remove the pyrogallic acid is much less than is required in the silver process to remove the hyposulphite of soda.
If it be the fact, however, that the solution of campeachy wood is more readily removed, that will no doubt be a great advantage. The writer in The Times recommends the use of albumenised paper, but I have found that the chromate of copper adheres to it rather strongly, causing a loss of time in extra washing. Otherwise, of course, it will give the print a more finished appearance.
Lacock Abbey, December 5th, 1864.
H. Fox Talbot
Notes:
1. The uranium-based printing-out paper invented by Jacob Wothly of Aachen, 1864, initally created quite a stir. It was considerably more sensitive than the albumen paper then in general use, but the claim for permanence was not fulfilled, and it was soon abandoned.