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During 1936 Agfa Ansco earnestly endeavored to contribute to the general progress of the photographic industry, not only by improving the quality of its standard products, but also by suggesting and creating several new emulsion types, such as the Infra Red “ A and the 35 mm. Reversible
Superpan, and the Direct Duplicating film.
The reader will find in this issue supplementary information in regard to the characteristics and application of these emulsions.
In addition, Agfa Ansco has also continued to engage its research chemists in extensive experimental work on various other problems of interest to the photographic industry. Most of this work, naturally, is unknown to the public, as it usually is kept confidential until it reaches the point of results.
One of the outstanding papers presented during the fall meeting of the 1936 5. M. P. E. Convention deals with a new method of hyper sensitizing photographic emulsions, which has been discovered and studied by Agfa Ansco scientists. This abstract has created such comment and interest that we feel justified in reprinting it. slightly abreviated, in this issue.
New Method for the Dry Hypersensitization of Photographic Emulsions"
By F. DERSCH AND H. DURR
SUMMARY. — Hypersensitization by mercury vapor increases the speed of photographic negative emulsions about 50 to 150 per cent, depending upon the emulsions used for the treatment. The important features of this method that make it superior to the well known wet-hypersensitizing methods are:
( I ) The film does not have to be put through a bathing process and then dried. (2) The mercury vapors are active also upon tightly wound spools of film, the sensitizing effect being uniformly spread over the whole length (e. g„ of a 1000-foot roll of 35-mm. motion picture film). If sufficient time is available for hypersensitizing, the films need not even be removed from their original wrappers, as the mercury vapors diffuse sufficiently through the wrapping material. (3) The increase of sensitivity is general throughout the range of wavelength of light to which the film was originally sensitive. (4) Not only can unexposed film be hypersensitized by this method, but it is also possible to intensify the latent image with mercury vapors. (5) The stability of the film is not permanently affected, although the increase in speed is gradually lost over a period of four weeks of aging. The clearness, however, remains the same, and may even improve somewhat. By a second treatment with mercury vapor the hypersensitization can be renewed in a film that has recovered from previous hypersensitizing.
After the introduction of panchromatic emulsions, methods of increasing the sensitivity of these emulsions by special treatments became generally known by the name of "hypersensitization." These methods were based upon the wellknown fact that the sensitivity of photographic films and plates can be increased by bathing them in water or in solutions containing small amounts of ammonia. Later, other solutions were recommended for the purpose; for example, solutions containing small amounts of silver nitrate and hydrogen peroxide, and so on.
* Journal of S. M. P. E.. Feb., 1937.
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