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July 31, 1863.] THE PHOTOGRAPHIC NEWS. 363 be a very unimportant consideration, if the process turn out as successful in general practical operation as it has done in our hands. PHOlO-ENGRAVING. The vast economic value of a thoroughly good and simple method of photographic engraving can scarcely be over estimated, and from the earliest history of photography efforts have been made, with more or less of success, to secure such a process. Most of our readers are familiar with the various methods attempted, from Fizeau’s process of etching Daguerreotype plates down to a recent date. Whilst recently in Paris we saw specimens, apparently of much promise, of two new processes of photographic engraving, the details of which, however, were not stated. A month or two ago we were favoured by a visit from M. Do la Blanchere, who showed us a number of exceedingly fine proofs from plates produced by his “ heliographic machine.” They consisted of portraits, about 10 by 8, of public men popular in France, from fine negatives by Nadar. As pictures and portraits they are exceedingly fine—bold and artistic, and, at the same time, full of photographic half-tone. They are, we are assured by M. De la Blanchere, entirely untouched. At the same time, they bear throughout the marks of a tool sufficient,to induce at the first glance a doubt of this state ment. These markings of the tool are, however, probably due to the treatment of the plate by the method adopted by mezzo-tint engravers, and they are doubtless really untouched, so far as that term is meant to imply that the plates arc not worked upon by the engraver, and that they owe nothing to the hand of man. A bitumen process is employed in ob taining the plate, and the whole result, which is very fine indeed, is, we are assured, due to the action of light and the “ heliographic machine.” The best example of photo-engraving which wo have yet seen, however, is by a process invented by Mr. D. C. Dallas, a gentleman who was associated at one time—to his cost, as he informs us—with the Photo-galvanographic Company, which came to grief some years ago. A specimen before us, “ Kenilworth Banqueting Hall.” from a negative taken expressly for the purpose by Mr. Bedford, is, we are assured— and the print bears evidence to the fact—from an entirely untouched plate. It has excellent gradation of half-tone, and is bold and vigorous. A few touches by a skilled en graver would make it a perfect picture. We have it here exactly as produced by chemical action, in order to illustrate the capabilities of the process. We regret that, owing to the unsatisfactory protection afforded by the existing Patent Laws, Mr. Dallas, at present, does not perceive any method of reimbursing himself for the cost—some thousands of pounds—of his initiatory labours, except in keeping the working and secret of his process in his own hands. We subjoin his communication on the subject:— In consequence of the very questionable protection afforded by the Patent Laws, I deem it advisable at present not to publish the details of my process. I have already sacrificed much to the “idea” of engraving photographs, and as I believe I have now solved the problem in a satisfactory manner, 1 am naturally anxious to remunerate myself. At a future time 1 may make a proposal, the effect of which, if agreed to, will bo to enable others to work my process. From the encomiums passed by highly qualified judges on the specimen I now submit—Kenilworth Banqueting Hall, from a photograph by Bedford—I think I am warranted in saying that I have solved the problem of successfully engraving photographs. But I should not consider myself entitled to the merit of this discovery were the specimen above mentioned touched up by the graver, or even the result of a happy chance. I am glad to bo in a position to say that the specimen has only required careful cleaning, and that unless my head and my hands fail me the result is certain. I can guarantee to produce, in a period varying from one to three weeks, an engraved plate from a photograph. In this plate, that which constitutes the essence of the photograph and the despair of hand labour—fac simile even to minute and almost microscopic detail—shall bo present. To attain this result, all that I require is a good re versed negative (easily produced by reversing the glass), and a positive print merely fixed with hypo, not toned. The methods which have hitherto given most promise are the bitumen process, photoglyphy, and photogalvanography. The other processes of photolithography and photozincography, from their very nature, cannot rival the richness of plate printing. The bitumen process and photoglyphy are essentially etching processes, and involve much hand labour and con sequent loss of fidelity. Photoglyphy is the least satisfactory of the two, as the etching ground employed is of a very deli cate nature, and the photographic chemical, bichromate of potash, has the unfortunate quality of destroying detail, the longer it is submitted to actinic influence. The most important step in advance was photogalvanography. This process came into my hands when in a most crude and impracticable condition, and after it had been given up as useless by others. By much patient labour I succeeded in making it practical, and the process has ever since been worked with the improvements which I effected. I was not permitted to reap the fruit of my labours, and after a considerable sum had been expended, by my then partners, to develop the process in a direction to which it was wholly unsuitable, the process has been almost abandoned. Photogalvanography, like photoglyphy, depends on the pecu liar action of bichromate of potash, in combination with gela tine. In this lies its weakness. It loses detail—the more so as it requires a very long exposure, sometimes upwards of six hours, and then without any certainty that the right exposure has been attained. There are consequently numerous failures from this one cause alone. I experimented long with this process, and found that the result was due to chromic acid. In other words, that with a composition merely of chromic acid and gelatine, a raised imago with granulation could bo produced. From this raised image the electrotype plate was subsequently made. Inde pendently of the loss of detail, and the uncertainty in the ex posure—both defects inherent in the process—the granulation was of a peculiar zig-zag and wiry character, which was of great value in the vigorous parts of the picture, but became broken or unconnected in the half-tones and fine details. This led to a pretty free employment of the graver and roulette, just in the very parts which made hand labour expensive. The process, indeed, was never capable of the high flight which was attempted, and, as I predicted, it broke down. Where expense was no object, the graver was a groat assistance, but it lessened the value of the facsimile. In photoglyphy and photogalvanography, the results are obtained from a positive impression. It was after experimenting some time with photogalvano graphy that it occurred to me to strike out in a different direction. Any one acquainted with engraving is aware that aqua-tint and “chalk," or stippling, produce fine grain, half tones, and detail. The problem 1 set myself was, how to imitate this combination. The aqua-tinter employs common resin dissolved in spirits of wine. This poured over his plate evapo rates, and leaves numerous globules of resin attached to the surface. The size of these globules depends on the proportion of resin to spirit. When the acid is put on the plate the resin acts as a resist, and a tint is produced in the intermediate parts. If the plate were now electrotyped before the removal of the resin, and a print taken from the electrotype, the resin parts would give a kind of stipple, or “chalk” marks, inter spersed with tint. It is something similar to this which I have succeeded in imitating, with peculiarities sui generis, by photo graphy and the electrotype. I can also, as it were, modify the size of the dots, obtaining them so fine as to carry almost microscopic detail; but if too fine there will bo deficient depth in the dark. In this as in all things there is the happy medium, and this I believe I have secured. I commence with the negative. This should bo reversed. From the negative a positive proof is taken; this I prefer not toned, but merely fixed in the sepia colour by the “ hypo.” I cover the negative, which must be varnished with a material from which I obtain a latent positive. This latent positive I turn by a simple process into a suitable negative, and it is with this negative that I sub sequently manipulate. I can time the exposure to a nicety, a few seconds over or under making an inappreciable difference. The excess or deficiency must not, however, extend to minutes
