An Old Discovery Revived in Photography.

Manufacturer and builder 10, 1870

The photographic journals contain a report of a communication lately made by Bazin to the Photographic Society of France, that the time of exposure in the camera may be diminished one third by admitting red diffused light on the plate, during or after exposure. He admits it into the camera by making in the four corners surrounding the lenses four round holes, closed with ground glass colored red by a solution of carmine in ammonia. Some twenty-eight years ago, Fizeau published the fact that when the time of exposure of the daguerrean plate was supposed to be too short, all that was necessary was to expose the plate to red light, which has the power to finish or hasten the chemical action commenced by the chemical rays, notwithstanding that pure red light alone is totally incapable of making any photographic impression. This was acted upon by ourselves and many other daguerreotypists twenty-five years ago. Either we used a box provided with red glass to expose the plate to red light after the exposure in the camera, or a part of the camera itself was provided with a few openings covered with red glass in order to admit the light during exposure. As the period of exposure was, however, only shortened one third at the most, it was not considered worth while to make use of the process, and the supposed improvement was dropped and soon forgotten.

It now appears to be rediscovered and published to the photographic world as above stated. It appears that the action takes place equally, whatever the manner of preparing the plate. Mr. Bazin states that the effect is produced with any formula, for preparing collodion or bath. We can readily believe this, as the red light acted equally well on the iodized silver plate of the daguerrean process, when collodion and bath are out of the question.

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