NOTWITHSTANDING that the collodion process, particularly in its wet state, rendered such important services to photography, it is today almost wholly a thing of the past. The later generation of photographers, indeed, know little or nothing about it, and probably the majority would not know how to use it if they wished.
As early as 1850 Poitevinafter Daguerre and the two Niepces perhaps the most fertile of the earlier French experimenters in photography, and one to whom the art-science owes a great dealsuggested the use of gelatine as a vehicle in place of collodion, the dangerous nature of which, apart from other drawbacks, was always felt to be a disadvantage. He did no more, however, than throw out the hint; and it remained for others, either independently or acting upon his suggestion, to prosecute the line of research thus indicated.
Many busy brains and cunning hands were soon at work on the problem; although it was not until 1871 that Dr. Maddox of Southampton succeeded where others had failed. In the month of September of that year he published in the British Journal of Photography a note on the production of an emulsion, the chief ingredients of which were gelatine and bromide of silver. Thirty grains of gelatine were swelled in cold water, and then dissolved by the application of heat, four drachms of pure water and two drops of aqua regia being added. Into this solution were then cast eight grains of cadmium bromide and fifteen grains of nitrate of silver, the result being a fine milky emulsion of silver bromide.
Plates that had been given a thin coating of this emulsion and then dried, upon being exposed beneath a negative, showed a faint but clear picture when developed with a solution of pyrogallic acid.
Maddox’s experiments were not completely successful, the reason being, as would appear, at least in part, the presence of nitric acid (caused by the aqua regia), which, acting as a restrainer, made the plates slow. Had he carried his investigations a little further he would doubtless have been able to overcome the defects in his process ; but all the available time he had at his disposal appears to have been taken up with photo-microscopy, and he had perforce to relinquish to others the line of research thus set afoot. Publishing his results, therefore, he left the matter for others to think over and work out to a more complete and satisfactory issue, remarking that ” so far as can be judged, the process seems quite worth more carefully conducted experiments, and, if found advantageous, adds another handle to the photographer’s wheel.”
Amongst others who took the hint thus thrown out and worked at the problem involved, were Kermetter abroad and Burgess and Kennett in England, all of whom produced a commercial article, though without deriving much benefit therefrom. The fact is they just failed to reach complete success. The difficulty with Burgess’s emulsion was that it was apt to decompose at anything like a high temperature. The presence of soluble salts was the trouble. These Kennett endeavoured to remove, and he patented a compound of “an aqueous solution of gelatine, together with a bromide, chloride, or iodide, and nitrate of silver,” which “is cleared of certain salts,” formed during the mixing, and then dried.
Both Burgess and Kennett prepared dry-plates, but commercially they were not a successpartly, no doubt, because they were a little before their time. Older photographers, who remember their introduction, will often recount, with an amused smile, how much they were beyond them. Their training in the old methods had been such that they could not understand their rapidity. They would spoil plate after plate, simply because of their inability to give them a sufficiently quick exposure.
Doubtless, the plates, too, were somewhat to blame. The fact is, that the time was not yet ripe for the perfect emulsion, because our knowledge of silver bromide was not sufficiently complete.
Perhaps it is worth while to note here that brominea deep reddish-brown liquid, fuming strongly at common temperatures, and found in sea-water combined with magnesiumwas only discovered in 1826, and that it was not until the publication of the researches of the Belgian chemist Stas in regard to chloride and bromide of silver that the world was made acquainted with the fact that the sensitiveness of bromine to light is greatly intensified by the application of heat.
It was the realisation of this fact by Mr. Charles Bennett, an amateur photographer of London, that finally solved the problem of a gelatine emulsion. By boiling his different solutions at a temperature of 90 degrees, he succeeded in making an emulsion that enabled him to obtain results which were a surprise to all who saw them, not merely on account of the quality of the pictures themselves, but from the rapidity with which they were taken. He very generously made public his process. This was in the early part of 1878, and, within a few weeks of the publication thereof, gelatine dry-plates had been manufactured and put on the market by several leading firms of photographic material manufacturers.
The effect produced by the introduction of the gelatine process was second to nothing that had gone hefore in the history of photography. It caused a complete revolution in the art, and, necessarily, in much of the material and apparatus whereby its results were achieved one of the minor, though still important, changes produced, being a saving in cameras, which were so rotted and deteriorated by the wet plates. These may be treated together, seeing that the changes that were brought about in the form and interior mechanism of cameras, in order to meet the increased rapidity of exposure, and by the augmented resources of the art in regard to picture supports, are but branches of the same subject.
The “new things ” in photography come so quickly one after another that we are apt to for-get the sensation of yesterday in the novelty of today. Yet it is but a few years since the photographic world enjoyed more than a nine-days wonder in what is known as the roller-slide, with its accompanying paper or film support.
The history of these things, like most else in photography, is one of gradual evolution; one idea being thrown out here and another therethe two then lying in wait for the development of a third. As early as 1854, we have the first germ of the roller-slide in a patent taken out by Spencer & Melhuish. Though crude enough in its general mechanism, the idee mere was present in the two rollers within the frame of the camera, one of which held the supply of sensitized paper, while the other received it as soon as it had been exposed, length by length, and received its picture. In this way, a succession of pictures could be taken on a long strip of sensitive paper. Although this invention appears to have had some successa qualified success as an ingenious noveltyit was unquestionably before its time.
About the same period, several other workers were exercising their wits in the like direction, and notably Captain Barr in India. But it was reserved for Warnerke to give the world what was in reality the first practical roller-slide. His own description of the contrivancepublished in 1875gives its principal components as “two rollers on which the sensitive film is wound,” which afford room for one hundred plates.” By this he means that, ” before the film is attached to the roller, it is divided into sections corresponding with the size of the plates by black lines drawn in pencil or otherwise.” Through the instrumentality of a darkened glass plate in front, in the place corresponding with the focussing surface, the sensitive film was guided in its progress from one roller to the other, and secured in its proper position. The film was wound from one roller to the other by means of metallic heads to the rollers. Exposure was obtained by a sliding shutter, and in the shutter was a tiny orange-glass window, for the purpose of observing the black lines on the film, and so securing the sections in proper position.
The roller-slide was only made possible with the introduction, or rather the revival, of sensitive film supported, not on glass, but on a flexible material. As we have seen, Fox-Talbot made use of paper for his negatives; and al-though paper was superseded by glass when the collodion process became popular, yet photographers were not slow to recognise that such a brittle substance as glass possesses serious disadvantages. Investigators endeavoured to find or to produce some material which, while possessing the transparency of glass, would be lighter and of a less brittle nature. Amongst others, Woodbury turned his attention to this problem, and in 1876 succeeded in manufacturing such a compound from Canada-balsam, collodion, and castor-oil.
This mixture, after being spread on a sheet of glass and allowed to dry, was coated with a sensitive emulsion and again allowed to dry. It was then taken from its glass support and cut into lengths for use in the camera. Although the inventor did not go beyond this, he threw out the idea that the film, being perfectly flexible, and hence capable of use in long bands, might, by means of rollers, be submitted in suitable lengths to the luminous image, and thus the inconvenience of changing plates be dispensed with by the turning of a handle outside the camera.
Warnerke took up this idea, and, though on the first appearance of his roller-slide he used paper coated with collodion emulsion, on the introduction of the more highly sensitive emulsion, which would not permit of the use of orange-glass windows, a further stage in the evolution towards the instantaneous camera was reached.
Besides the advantages of lightness and non-fragility, film photography possesses another superiority to glass, and that is its freedom from halation–the term applied to a certain blurring of the image caused mainly by reflection from the back surface of the glass support. In glass negatives it is shown by an encroachment of the light portions upon the dark, as, for instance, in taking a window, where there would be an invasion of light upon what should be dark all round the edge.
The rapidity of the dry-plates and the film is such that cameras specially constructed for the purpose can be held in the hand during the operation of exposure. Much ingenuity has of late years been given to the development of the capabilities of the camera in connection with the use of dry-plates. The forms the dark-box ” has taken under the new requirements are almost uncountable. For small-sized photographs various contrivances have been adopted whereby the camera itself becomes a storage for plates, a simple mechanical arrangement permitting the exposed plate to be transferred to the back, while another takes its place. The ” magazine camera,” as it is called, possesses certain undeniable advantages, though it is outdone by the roller-slide camera when the film used in the latter can be thoroughly relied on, which, unfortunately, is not always the case.
While, therefore, for ease and the rapidity with which successive exposures can be made and views taken, nothing comes up to the hand-camera with the roller-slide and film, for sure work the magazine camera is, on the whole, preferable. It forms no part of the scheme of this work to enter into the respective merits of cameras ; there are many excellent ones in the market ; but for hand as well as tripod use, Newman & Guardia’s instruments cannot easily be beaten. They are provided with good lenses, and have all the special features of a first-class tripod cameravertical and horizontal rising fount, extension to double or triple the normal focus of the lens, iris diaphragm, hand and pneumatic releases, etc.
Another development which has arisen out of the extreme sensitiveness of the dry-plates is what are known as flash-light pictures. These are photographs taken by means of the almost instantaneous flash of light produced by scattering powdered magnesium in the flame of a lampof which there are many specially contrived for the purpose. There is generally a receptacle attached for holding the magnesium powder, which is carried into the flame by means of a pneumatic ball and tube. Very effective pictures of groups and of children are taken in this way. Exposure is generally managed by pressure of the pneumatic ball, which puffs the powder into the flame, so that the simultaneity of the two operations is as nearly as possible perfect.