THE next important advance in the chemical department of photography, after the introduction of albumen on glass plates, was the invention of the collodion process. Collodion is a viscid compound composed of soluble pyroxyline dissolved in ether, to which alcohol is added. When poured upon a plate of glass it runs freely over the surface, and, the ether and alcohol evaporating, the collodion is left behind in the form of a tough translucent film.
M. Le Gray appears to have been the first to suggest the employment of collodion as a vehicle for holding the sensitive salts. In a book published in 1847, and translated into English in the following year, he says: ” I have just discovered a process upon glass by hypofluoric acid, the fluoride of potassium and soda dissolved in alcohol, forty degrees Fahr., mixed with sulphuric ether, and afterwards saturated with collodion; I afterwards react with nitrate of silver, and thus obtain proofs in the camera in five seconds in the shade. I develop the image with a very weak solution of sulphate of iron, and fix with hyposulphite of soda.” A similar hint as to the value of collodion was made about the same time by Robert J. Bingham, an assistant of Faraday. But it is to Frederick Scott-Archer that the world is indebted for the practical introduction of this method of photography.
Scott-Archer was a sculptor, and he appears to have taken up photography in order that he might preserve records of his works. How he came to turn his attention to collodion is not known; but towards the end of 1850 he had so far succeeded in the working out of his process that he made it known to some of his friends, and amongst others to Mr. P. W. Fry, the photographer, from whom in particular he received much assistance, and to whom much is due for its successful application.
The results obtained by collodion were so greatly in advance of anything that had hitherto been achieved in practical photography that it may be said to have established the art on its present basis. It almost immediately came into very general use, and many adepts in chemical manipulation gave much time and attention to improve the methods of making the compound, and to discovering the best ways of using it.
One method of preparing the collodion is by soaking clean cotton-wool in nitrate of potash. When thoroughly soaked, the excess of nitrate of potash is removed, and a quantity of sulphuric acid, to which a small quantity of nitric acid has been added, poured over it. The next operation is to take out the cotton and wash it thoroughly in running water, after which it is freed from water by squeezing, and then dried. It is now the well-known gun-cotton or pyroxyline, and may be dissolved in sulphuric ether in the following proportions:
Sulphuric ether 18 fluid ounces. Alcohol . 6 drachms. Pyroxyline 30 grains. Solution of ammonia 5 drops.
The solution obtained is collodion, and when some soluble iodide, and a little potassium bromide have been added, it is ready for use.
In the early days of collodion many of the leading photographers prepared their own, and had their own ways of doing it. To say nothing of its dangers, it was a tedious process, and caused the early photographers an amount of toil and trouble of which the men of today have but little conception.
When poured upon a plate of glass collodion freely runs over the surface. Two or three minutes is sufficient for the film to set. When coated the plate was immersed in a bath of silver nitrate for about a minute, during which time silver iodide was formed in the pores of the collodion. The plate was now ready for exposure in the camera. Development was usually effected by means of pyrogallic acid, the power of which in bringing out the latent image Archer claimed to have been first made known by him, and the picture was fixed by soaking the plate in hyposulphite of soda, though at a later period cyanide of potassium was generally preferred, because of acting more quickly; a thorough cleansing in running water followed. After the plate had been allowed time to dry, the last and completing process, before the negative was handed to the printer, was to protect the film from abrasion by a coat of varnish.
Collodion gradually pushed its way, and by 1854 its use had superseded almost all other methods with the general photographer; for by this time photography had become a profession. With collodion, too, the amateur was able to take the subject up, and during the next few years photography became very popular with people who love a hobby, and who, in the case of photography, did a great deal towards perfecting its methods.
By this time, however, the inventor of the process, who at first appears to have thought so little of it that he did not protect it by a patent, was in his grave. He had made so little out of his invention that his family were left almost destitute. A timely subscription, however, and a government pension of £50 per annum, saved the children from want.
The almost inestimable value of collodion was hardly established before the many shortcomings attending its use began to be perceived, and attempts made to remedy them. One drawback connected with its employment was the necessity that the glass plates coated with the sensitized collodion should be exposed in the camera while wet, and, further, that the exposed plates must be developed before the surface had had time to dry. For this reason the wet collodion process, though suitable enough for the studio, was ill-adapted for outdoor work, while for travellers its use was almost an impossibility. If it was desired to take a photograph of an interior, where, on account of the dim light, a long exposure was requisite, the surface of the plate had time to dry before the task was accomplished, the result being that the plate was spoiled, for the simple reason that the silver iodide crystallises when dried in contact with the nitrate of silver, and so makes a spotty negative. In cold weather the silver nitrate solution was too slow to work.
Many attempts, and a great many suggestions, to overcome these and other defects in regard to the wet collodion process were made during the years immediately following its introduction. It is not necessary, however, to enter into them here. Suffice it to say, that ere long various methods were devised for keeping the prepared plates moist for a certain time. Nitrate of zinc, and then nitrate of magnesia were used for this purpose, and found to answer for a week or more by preventing crystallisation. A solution of honey, or grape-sugar, was employed for the same purpose, with some success. In lieu of anything better, these and similar processes were made use of for some years ; but a stepping-stone to a new and important advance was laid when Dr. J. M. Taupenot, a French scientist, made public a method wherein a solution of iodized albumen was poured over the collodionized and sensitized plate, which was then allowed to dry. The plate was then dipped a second time in a bath of silver nitrate, and again washed and dried. ” This was,” says Mr. W. J. Harrison,* ” the first dry-plate process of practical utility.” The philosophy of the process was that by its means the superabundance of the salt was washed away, and so crystallisation obviated.
The process was published in La Lumiere in 1855, and was soon after made known in England, where it was very popular for some time. The plates would keep for six or eight weeks; but the great drawback to the process was that it was slow. Taupenot’s method undoubtedly established the value of the dry-plate, and every effort was now made to improve it. After the publication of Dr. Taupenot’s collodio-albumen process in 1855, “every few months,” says Harrison, “saw the announcement of some new substance or other, wherewith the sensitive surface of a collodion plate might be covered, so as to enable it to be dried and kept ready for use.”
Dr. Norris of Birmingham appears to have been the first to make dry-plates a commercial success. He took out a patent for his process in 1856, and for ten years they had considerable vogue. According to his own description of his process, the film, after having produced in it the sensitive iodide of silver, “is immersed in a solution of gum arabic, or of dextrine, starch, gelatine, albumen, gum tragacanth, vegetable mucilage, caseine, gluten, or other such like substances, that will, by occupying the pores of the collodion film, prevent its condensation on drying, and retain it in a sensitive and pervious state ; the films are then dried, and are ready for exposure to light, or may be kept for any length of time and used as desired.” The plates thus prepared are said to have been nearly as rapid as wet collodion plates, and it is thought by some that the maker had ” discovered the superior sensitiveness of bromide over iodide of silver,” and that the rapidity of the plates was due to the use of the former.
A number of other dry-plate processes came into use during the same period, although they were all, without exception, slow as compared with the wet-plates. One of the most interesting of these was that first used by Major C. Russell, who, having employed gallic or pyro gallic acid for increasing the keeping powers and sensitiveness of dry-plates, was thence induced to try tannin, the substance from which those acids are derived, with the result that he found it better than them. Another valuable process was that devised by Captain Abney, and known as the “albumen-beer process,” which was used with success by the expeditions sent out in 1874 to study the transit of Venus. The secret of it lay in the use of a mixture of albumen and flat beer, with which the sensitized plate was given a wash.
Important, however, as these developments were at the time, they proved but stepping-stones to better things. One of the most striking facts connected with photography, indeed, is the rapidity with which it has passed from stage to stage. It speaks much for the intelligence of the men who successively took hold of it, either in its scientific or its art aspects, that within the century it has been developed from its first ineffectual beginnings to the position it now occupies as the hand-maiden of all the arts and sister of every science. No branch of science has leapt from callow youth to virile strength with such rapidity, and even yet it seems barely to have passed its adolescence.
Collodion emulsion was the next step onward. Very soon after the introduction of collodion it was foreseen that the next advance would be to a method whereby the silver nitrate bath could be eliminated. So early as 1853 a French photographer named Gaudin put forth the idea that ” the whole future of photography seemed to require a sensitive collodion, which could be preserved in a flask and poured, when required, upon glass or paper ; and by the use of which, either at once or after the lapse of time, positive or negative pictures could be obtained.”
This put succinctly in words a notion that must have been floating in many minds. Indeed before this statement appeared in print combinations intended to meet that end had been announced; but neither these nor Gaudin’s ” photo-gene,” as he called it, a compound of nitrate of silver dissolved in hot alcohol and added to collodion, met the need. And it was not until the latter part of 1864 that a really effective emulsion was devised. This was the production of Messrs, Sayce & Bolton of Liverpool, who, by adding nitrate of silver to a bromized collodion, developed silver bromide in the collodion. Plates coated with this concoction were given a wash of tannin and then dried.
This first rough draft, so to speak, was quickly followed by improvements until, some ten years after its first introduction, an emulsion was produced composed of pure silver salt and collodion, which could be kept in bottles for years. All that was necessary when the emulsion was required was to melt it by placing the bottle in hot water, and then to coat the plates with it and dry them. The ” Beechey Dry-Plates,” very popular for many years, and still in use, were made from a preparation very similar to the Sayce & Bolton emulsion.