COLLODIO-CHLORIDE PRINTING-OUT PROCESS.—• silver printing process in which collodion is used as the article to hold the silver salts. The name aristotype has also been applied to this process as well as to its sister process, the gelatino-chloride. It is also termed collodion paper.
The earliest experiments in collodio chloride printing were made as far back as 2864 by G. Wharton Simpson.* This gentleman attended a lecture given by Professor Roscoe, in which the latter stated that the action of light on chloride of silver paper was a reliable means of obtaining photometric measurements. Simpson declined to agree with this theory, and to prove the correctness of his objection instituted a series of experiments, using different media for holding the sensitive salts, as he contended, and rightly, that there would be a considerable change due to the proportion and character of the organic matter in this or the paper. The result of these experiments was the discovery of the collodio-chloride positive printing process, which was first published and a paper read before the London Photographic Society on March 14, 1865. In this paper Mr. Simpson claimed for this process many advantages over albumen. " First, the sensitive salts are all combined in one inert vehicle, no changing conditions exist; every specific portion of the vehicle used contains definite proportions of the salts, and the stock from which it is used is not impoverished or changed in any respect. There is no interchange of parts going forward at each step of the process as with sensitizing albumen paper. The last sheet coated from a bottle of the preparation contains on its surface the sensitive salts mixed in the same proportions as the first. There is nothing to prevent absolute uniformity of results." Simpson's communication of his process to the Photographic Society was received with unbounded enthusiasm, but notwithstanding this the collodion process never seems to have been taken up except by one or two experimenters.t It apparently died a natural death, or perhaps we should say went into a kind of trance, for it was not until years after that it was revived.
W. Terry, an American, added the fulminating compounds of silver to the emulsion. The addition of a few drops of the supernatent solution of strong ammonio-nitrate of silver, or oxide of silver dissolved in nitrate of ammonia to which alcohol was then added and heated to the boiling point, to even a bad emulsion of collodion chloride, had, Terry stated, been found to impart wonderful properties of fine color and brilliance.
A number of experiments were then made by different workers with the various chlorides more or less soluble in alcohol. Among these were those of cadmium, ammonium, barium, calcium, cobalt, sodium, strontium, lithium, magnesium, and zinc.
About the year 1884 Liesegang produced a fine collodion em ulsion for printing on paper, glass, etc. To the process he gave the name Aristotype—a name that seems to have adhered to it, although it has become rather confusing since the same title was given to the gelatino chloride process.
There is no country in the world, however, where the collodio-chloride of silver process is as popular as in America. In this country the manufacture of the paper has been taken up by several firms on a large scale and backed by considerable capital. All difficulties seem to have been surmounted and the paper turned out nearly perfect in every respect.
The difficulty with the curling caused by the expansion of the paper support appears to have been almost entirely surmounted.
The collodion papers of commerce are prepared chiefly upon the enamel or baryta paper, which serve to keep the sensitive film on the surface and so come into close contact with the negative, reproducing the finest details. Any ordinary white paper can be used provided it is chemically pure. We know of but few papers that answer this important condition. Rive's, Saxe's, and Steinbach's are of pure quality and can be used with safety; others must be experimented with.