[The original has not been located. It was published under the title 'Photographic Engraving' in the Athenaeum, no. 1328, 9 April 1853, p. 450.]
I beg to inform you that I have recently had the good fortune to advance another step in the path of photographic discovery; - and as I am in hopes that what I have accomplished will prove of great practical utility, I have drawn up the following brief account of it.
Attempts have been made by several ingenious persons, especially on the Continent, to complete the daguerreotype process by engraving the plate impressed with the photographic image; - that is to say, by causing it to engrave itself, by using chemical means only, and without requiring it to be touched in any way by the hand of an artist or engraver. Nor have these attempts been unsuccessful in themselves; - on the contrary, specimens have been at various times brought over from Paris quite sufficient to show that the thing is feasible. But the practical difficulties of execution have been such as to limit the utility of the invention; and I understand that the plates have been found to wear out after affording but a small number of impressions.
I have been so fortunate, however, as to discover a method which I believe to be entirely new of solving this interesting problem, which already in my hands succeeds with a reasonable degree of certainty for a large class of photographic objects, and which will doubtless be soon and greatly improved by other experimenters. I am now engaged in drawing up a full account of the process, <1> which will be ready for publication in a few weeks; but in the mean time I trust you will permit me to sketch a general outline of the subject.
I will begin by referring to the labours of those who have preceded me in this line of research. The first person who turned his attention to this subject was Dr. Donné <2> of Paris, about the year 1840: - as appears from the Comptes Rendus of the Academy of Sciences. I believe, however, that his attempts were not crowned with much success, and were soon discontinued. I have not seen any of the specimens which he executed. Dr. Berres, <3> of Vienna, was, I think, the next to take up the subject. The specimens of his engravings which I have seen are of small size; they exhibit considerable sharpness in the outlines, but no half tints or gradations of shade, - the want of which produces a harsh effect. I understand that Dr. Berres' secret has never been disclosed. After him, the subject was resumed by M. Fizeau, <4> of Paris, with considerable success. Some specimens which I have seen stated to have been made by him, are beautifully distinct. But notwithstanding that his process was taken up with a view to its improvement by more than one eminent photographer in London, I believe that its use has been discontinued owing to the great uncertainties which attended it and wearied the patience of the experimenters. There may perhaps have been some other experiments published; - but the above mentioned are the chief processes of which I have seen specimens or met with any published account. Some months ago I resolved to take up this curious problem as offering an interesting field of research and delicate experiment.
Abandoning the methods hitherto employed, which had not been found in practice sufficiently successful, I entered into a new path, - which shortly gave me hopes that I was proceeding in the right direction. But as I advanced, difficulties appeared to multiply; and I found that on various occasions the results were most anomalous and contrary to all expectation. For instance, when I had prepared everything as I thought, to produce a positive etching of an object; the result was a negative etching of it. At other times half the plate was etched positively, and the other half negatively; - and of course such a result remained useless for any practical purpose. I here employ the term positive etching, which I believe has not been used before, to imply an etching of such a kind that the impressions struck off from it represent the objects positively, or as they are in nature:- and of course I employ the term " negative etching" in the opposite sense. The anomalous results which I at first obtained obliged me to submit to a careful investigation the photographic properties and the chemical re-actions of a considerable number of substances, - until at length the principal facts observed were satisfactorily explained, and the nature of the disturbing causes being known, the process was brought under control. And it was found that by comparatively slight changes in the mode of manipulating, either a positive or a negative etching could be produced at pleasure. But, of the two, the positive was the more perfect, and appeared also to be much more manageable than the other; which principal point being ascertained, I thenceforward devoted my attention chiefly to the perfecting of the positive process. I have now to mention to what point I have as yet succeeded in improving it. The objects most easily and successfully engraved are, those which can be placed in contact with the metallic plate, - such as, the leaf of a fern, the light feathery flowers of a grass, a piece of lace, &c &c. In such cases the engraving is precisely like the object; so that, I would almost seem to any one, before the process was explained to him, as if the shadow of the object had itself corroded the metal, - to true is the engraving to the object. If a veil of black crape is laid upon the metal plate, every thread of it is engraved with wonderful precision and distinctness; and if two thicknesses of the crape are placed upon the metal, obliquely to each other, still the resulting engraving offers no confusion, but with the help of a lens the lines belonging to each of the folds can be distinguished from those of the other.
Objects which cast a broad and uniform shadow - as, for instance, the opaque leaf of a fern or other plant - produce an etching which when printed off delineates the original in a pleasing but unusual manner, - something between an aquatint engraving and an Indian ink drawing. But I have no doubt that a great variety of other effects will be found to be obtainable from the process. When the object to be copied is a photograph on paper, the process offers some difficulties which have not yet been entirely surmounted. Not that the engravings thus obtained are deficient in accuracy, - for they follow the original with considerable minuteness of detail; but because the gradations of shadow and the depth of the etching upon the plate are found not to follow the same law as they do upon the original photograph. There is a much greater difference on the plate than exists in the original: - the shadows are too deep, and the lights are too strong. I am not without hope, however, that means of avoiding this may be discovered when the process shall be better understood. Some change or other in the manipulation may possibly be found to abolish this law of variation in the intensity of the shadows, and to substitute another more in conformity with nature.
I must not pass over a leading feature in my new process. It is this: - I find that the size of the plate to be engraved makes no difference in the result of the process except that it necessitates, of course, a greater degree of carefulness in the operator. Consequently, whatever degree of accuracy is obtainable on small plates is likewise obtainable on large ones: - and this is a fact of considerable importance. For, - the advantage of this new mode of engraving, - the quantity of objects and details represented increases in proportion to the area of the picture, while the error or inaccuracy which affects each individual point is of constant magnitude. In large plates minute deviations from the outlines of the original, even if they exist, are of little consequence. They are merged and disappear in the general effect.
I am, &c.,
H. F. Talbot
Lacock Abbey, April 4.
1. It would become known as photographic engraving.
2. Dr Alfred Donné (1801-1878), professor of microscopy.
3. Josef Berres (1796-1844), professor of anatomy and microscopist.
4. Armand Hippolyte Louis Fizeau (1819-1896), French physicist.