[The original has not been located. This is from the printed version, published in The Literary Gazette, no. 1258, 27 February 1841, pp. 139-40.]
CALOTYPE (PHOTOGENIC) DRAWING <1>
To the Editor of the Literary Gazette
I will now proceed to give you some further details, for which I had not room in my last letter, <2> respecting the phenomena which occur during the very singular photographic process to which I have given the name of Calotype. And I may as well begin by relating to you the way in which I discovered the process itself. One day, last September, I had been trying pieces of sensitive paper, prepared in different ways, in the camera obscura, allowing them to remain there only a very short time, with the view of finding out which was the most sensitive. One of these papers was taken out and examined by candlelight. There was little or nothing to be seen upon it, and I left it lying on a table in a dark room. Returning some time after, I took up the paper, and was very much surprised to see upon it a distinct picture. I was certain there was nothing of the kind when I had looked at it before; and, therefore (magic apart), the only conclusion that could be drawn was, that the picture had unexpectedly developed itself by a spontaneous action.
Fortunately, I recollected the particular way in which this sheet of paper had been prepared, and was, therefore, enabled immediately to repeat the experiment. The paper, as before, when taken out of the camera, presented hardly any thing visible; but this time, instead of leaving it, I continued to observe it by candlelight, and had soon the satisfaction of seeing a picture begin to appear, and all the details of it come out one after the other.
In this experiment, the paper was used in a moist state; but since it is much more convenient to use dry paper if possible. I tried it shortly afterwards in a dry state, and the result was still more extraordinary. The dry paper appeared to be much less sensitive than the moist; for when taken out of the camera after a short time, as a minute or two, the sheet of paper was absolutely blank. But, nevertheless, I found that the picture existed there, although invisible; and by a chemical process analogous to the foregoing, it was made to appear in all its perfection.
After several further experiments, which were requisite in order to come to a right understanding of this unexampled natural process, I found it expedient to abandon the former method of taking views with the camera, in favour of the new one, so far excelling it in rapidity and power. The result of my experience hitherto with this calotype paper is, that if properly prepared, it will keep three or four months, ready for use at any moment, and moreover it is used in a dry state, which is a great convenience.
The time of exposure to light in the camera maybe varied, according to circumstances, from a quarter of a minute upwards; and the paper, when taken out of the instrument, appears quite blank, as I said before, but it is impressed with an invisible image. It may be kept in this invisible state for a month or so, if desired, and brought out, or rendered visible, when wished for. But, generally, this is done shortly after, or at least on the same day, for fear of accidents (such as a casual gleam of daylight, which would at once annihilate the whole performance). Whenever it is desired to render the picture visible, this is done in a very short time, as from a minute to five or ten minutes, the strongest impressions coming out the easiest and quickest. Very faint impressions (as those obtained when the paper has been only a few seconds in the camera, or the objects have been not luminous enough) take a longer time in coming out, but they should not be despaired of too soon, as many of them exhibit difficulty at first, as if reluctant to appear, but nevertheless end by coming out very well. The operator of course remains in a darkened room, lit by candles only.
I know few things in the range of science more surprising than the gradual appearance of the picture on the blank sheet, especially the first time the experiment is witnessed. The operator ought to watch the progress of the picture, until, in its strength of colour, sharpness of outline, and general distinctness, it has reached in his judgment the most perfect state. At that moment he stops further progress by washing it over with a fixing liquid. This is washed off with water, the picture is then dried, and the process is terminated.
The picture is found to be very strongly fixed, and from it numerous copies may be taken on common photogenic drawing paper, by the method of superposition in sunshine. The original picture does not readily become altered, or wear out by this exposure to the sun; but in case it does so, as happens sometimes, I find that it may be in general readily revived. This revival, which is a most curious particularity of the calotype process, not only restores the picture to its pristine strength, but frequently causes fresh details and minutiŠ to appear in the picture, which had not appeared before, at the time when it was first brought out, or rendered visible (owing to that process having been checked too soon). These details, therefore, had been lying in an invisible state on the paper all this time, not destroyed (which is the most extraordinary thing) by so much exposure to sunshine. They were protected by the fixing liquid. But no one could have supposed beforehand, or without ocular demonstration, that it could have exerted so complete a protecting power. This is an invaluable property of the calotype - the power of reviving the pictures - not only because it allows so many copies to be made, but because it enables the artist to correct the error of his judgment, in case he has made too faint a picture at first, by stopping it too soon while it was coming out.
Some further details on this subject, and an account of the chemical processes employed, I reserve for a paper which I intend to lay before the Royal Society.
I am, &c. &c.
H. F. Talbot
Feb. 19, 1841.
1. Calotype used as a modifier of the term photogenic drawing was not taken up and is rarely found in the literature.