DRY PLATE PHOTOGRAPHY
THE TANNIN PROCESS,
MADE SIMPLE AND PRACTICAL
FOR OPERATORS AND AMATEURS
BY JOHN TOWLER, M. D.
New York and London: 1865
The peculiar advantages of Dry Plate Photography are but little understood by the ordinary photographic operator; and, when these advantages are understood and recognized, there is a difficulty in withdrawing the artist from the general routine of the wet process, whose results are so easily and quickly obtained, flash out as it were in a moment for adoption or condemnation, to bestow his attention on a process whose results are invisible, and depend entirely upon the educated experience of the workman and the accuracy of his workmanship, a structure, in fine, built upon faith.
There is a striking analogy between the two processes, wet and dry, and the two modes of printing, direct solar printing and printing by development. In solar printing albumen on paper, beneath a negative, the image appears gradually, and finally assumes all the necessary vigor; the operation of printing can be watched, controlled, and pronounced finished when the eye is satisfied. With a small quantity of experience the eye becomes the sole guide. But with development-printing the image is invisible; none of our senses can perceive its existence; it is a latent image; of this we are firmly convinced by an experience that has never met with an exception to the rule, we have therefore a lively faith in the result; in the latter case, therefore, experience and faith become our guides. They are equally our guides in dry plate photography.
The practical operator will find the dry process much more advantageous than the wet process in taking photographs of public buildings, architectural structures, gentlemen’s residences, country seats, farm houses, shipping, steam engines, machinery, monuments, in fine, all works of art and beauties of nature in still life in his own city or immediate neighborhood. Even if the operator should possess a portable tent, in the cases just enumerated the dry plates are to be preferred in every instance whenever a picture of a single building, etc., alone is required. The reason is almost self-evident. To lug or drag a portable tent and camera to the place in question; to mount them on tripods for operation; to place the collodion bottle, the bottle containing the developer, the water bottle, and the bottle holding the fixing solution, each in order; to expose, develop, fix, wash the plate, and stow it away in a safe place where no accident can befall it; to pack up again all these paraphernalia and retrace, with bag and baggage, the homeward path all these operations contrast very distinctly with that of carrying on the shoulder a small camera already screwed to its tripod, and ready for operation the moment the goal is attained. The camera is lowered, the view adjusted in focus, the picture taken before an accumulation of human youngsters can stop up the aperture of the lens or diversify the scene on the collodion plate with innumerable ghosts. The camera came and is gone before the inquisitive have had time to ascertain the cause of your appearance and departure.
Finally, transparent positives, opal or porcelain pictures, transparent stereographs, and photo-miniatures are very easily and beautifully prepared on dry plates, sometimes more easily than on wet plates, and in some instances where it is impossible to take them at all by means of wet plates. To print on glass, that is, on dry plates, has become one of the most enchanting operations in photography, as an evening recreation by gaslight. This light, or the light from a small piece of burning phosphorus, or a few spirals of magnesium wire, is quite intense enough to produce the required actinic effect on a dry plate in a few minutes. During the summer season — the season for trips and excursions — negatives accumulate to a great extent, and remain on hand unprinted until the dreary winter arrives, when nature lies buried in sepulchers, as it were, clothed in white raiment, and when homes become irksome without employment; now is the time, in the long evenings, with our wife and children around us, to bring the negatives from their niches, take impressions of each by the dazzling jet of light from the argand burner on the table, and recount to them, in the midst of such vivid illustrations, the stories and histories arising from scenes visited or renowned. This source of innocent and instructive pleasure is inexhaustible, its enchantment can not be described; it can be understood only by those who have participated in it.
The want of success in securing a picture on a dry plate has arisen principally from impatience and hurry, and the aim of dry plate photographers, being to shorten the time of exposure, has all along conduced to hurl beginners into the trouble alluded to. Be convinced that the sensitiveness of a dry plate is far inferior to that of a wet plate, five or six times less, that is, if a given lens with a given stop, light, and exposure, will produce a picture on a wet plate in twenty seconds, the same lens will require, under the same conditions on a dry plate, about two minutes at least, and most probably four minutes’ exposure would be no injury to the result sought. Do not be beguiled by any assertion of others, or any desire of your own to diminish the time of exposure; you will fail assuredly if you do, and will then condemn a good process. The dry plate requires a long exposure; and learn now that over-exposure is no injury, because there are means of controlling its effects, but there are no means of remedying an under-exposed dry plate, that is, of getting a picture on a film where light has failed itself to perform it’s part of the wonderful task. It is true that the alkaline developer, as it is called, has a tendency to shorten the long exposure, but it increases in the same ratio the chances of failure; and although we ourselves are delighted with the results of the alkaline developer, as well as with an alkaline treatment of the dry plate previous to exposure, we recommend it to our scholars not as a normal practice, but rather as a means to be adopted if we know beforehand that the time of exposure, by whatever circumstances, was too short.
It is desirable in dry plate photography to make use of flattened plate-glass, because it will frequently happen that you may desire to take transparent copies of your negatives on dry plates. In this case, the two surfaces, that is, the surface of the negative and that of the dry plate, which is intended to receive the picture, must be accurately in contact in every part. With common glass this condition can seldom or never be attained. The glass must be free from all sorts of flaws or imperfections, because it would be a great loss of time and material to go to the trouble of preparing a dry plate, and know beforehand that the result, nine times out of ten, with such imperfections staring you in the face, must inevitably be imperfect. Some dry plate photographers are so particular in regard to their glass, as never to use a plate that has already been once coated with the sensitive substances. This degree of refinement and care is, in our opinion, unnecessary, although we are willing to admit that better results are more likely to be obtained by such a precaution, and the ordinary mode of cleaning glass, than by using old plates over again; but if old plates be cleaned in the manner hereafter described, they may be coated several times in succession without any detriment to success.
The plates are raised from this bath in like manner, by means of slips of glass; they are then allowed to drain for a moment, and finally thoroughly washed in pure water, and placed on the draining racks to dry, if the surfaces are intended to be polished afterward; otherwise each is ready as soon as it is washed to receive the substratum of albumen, which is prepared as follows:
Separate the white of a single egg from the yolk, and beat it well up into a froth, then add to the froth six ounces of pure rain or distilled water and one drachm of ammonia. Shake the mixture very intimately together in a bottle, which must contain at least twice the quantity of material, that is, about a pint measure. The solution is next filtered through a tuft of cotton wool; it might be filtered through coarse filtering paper, only in this case the solution assumes a very slight tinge of straw color in passing through the paper. This arises probably from the fact that the sizing of the paper is dissolved by the ammonia. It is preferable to avoid this coloration, by using only a clean tuft of cotton inserted in the neck of the filter. The first part of the solution, to the amount of about an ounce, is poured back again into the filter, because it probably has taken down with it a few fibers of cotton, which would be injurious in the subsequent operations, if left on the film. The vessel, too, which receives the filtrate at this stage is carefully washed out with clean water, and the filtration is allowed to proceed to the conclusion.
The plate having been well washed, as already described, is either fixed on a pneumatic holder, or held by one corner, between the thumb and forefinger, as a plate is held for the reception of collodion. The albumen solution is then poured upon the extreme right-hand corner, and is allowed to flow, sidewise to the distant left-hand corner, and then downward toward the hand, driving before it the moisture still adhering to the surface, and passing off at the nearest right-hand corner, into the vial containing the solution. It frequently happens during filtration that innumerable small air bubbles are formed on the surface of the filtrate; this may partially be avoided by dipping the beak of the glass filter into the solution, or by not allowing the solution to fall more than half an inch or so before it reaches the vessel beneath. Should it so happen, however, that the albumen solution contains a quantity of these air bubbles, they must be blown away to the opposite side of the vessel before you begin to pour the solution upon the plate; otherwise, if you once get them upon the plate, you can rarely get rid of them without flowing the plate two or three times, a process which is likely to produce an uneven film and to generate a fresh crop of bubbles. In pouring the solution upon the plate, it is advisable to place the spout of the vessel near the surface of the plate, in order thus to obviate as much as possible the generation of these offensive bubbles, which if left on the film will produce transparent circles in the picture, visible after all the operations are ended. To coat the plate evenly and uniformly requires gentleness of action combined with the preceding directions; a quick and boisterous demeanor will not succeed at all.
It is universally admitted that the dry process requires a much longer exposure than the wet process; from our own experiments we make the deduction that this exposure, on an average, is at least six times longer with the former than with the latter. There seems to be a mania in photographers to aim rather to shorten the time of exposure than to get good results; and, owing to this morbid desire or aim, many tannin plates turn out to be so much trash. Let the operator, therefore, be thoroughly imbued with the idea that a tannin plate is slow in receiving the impression; but when once the impression is made, it can be developed. Furthermore, let him understand this fact, that an under-exposed tannin plate is irremediable, while an over-exposed tannin plate can be controlled, and the image developed accordingly.