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  1. #111
    smieglitz's Avatar
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    From Goethe's Farbenlehre (Theory of Colors):

    "Ritter discovered in 1801 that beyond the extreme violet of the spectrum there is a vast efflux of rays which are totally useless as regards our present powers of vision. These ultra-violet waves, however, though incompetent to awaken the optic nerve, can shake asunder the molecules of certain compound substances on which they impinge, thus producing chemical decomposition. But though the blue, violet, and ultra-violet rays can act thus upon certain substances, the fact is hardly sufficient to entitle them to the name of chemical rays, usually applied to distinguish them from the other constituents of the spectrum. As regards their action upon the salts of silver, and many other substances they may perhaps merit this title; but in the case of the grandest example of the chemical action of light- the decomposition of carbonic acid in the leaves of plants, with which my eminent friend Dr. Draper has so indissolubly associated his name-the yellow rays are found to be most active."

    So "chemical rays" are UV.

    And if Photography was restricted to only those images formed by the action of UV, the billions of images taken on ortho and panchromatic materials wouldn't qualify.

    In an age of Lambda printers and platinum prints generated using inkjet negatives as light attenuators, does it really make much sense to argue over the meaning of the word Photography? I think the energy is better spent actually ensuring that an inkjet print is identified as such and not as a carbon or platinum print.

    Joe

  2. #112
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    The basic sensitivity of silver halide is in the UV portion of the spectrum. Adding iodide increases sensitivity to visible light (blue region). Through the action of bromide, iodide, sulfur and gold, the inherent sensitivity to blue light is vastly increased, and the addition of sensitzing dyes extend sensitivity to green, red and infra red light.

    PE

  3. #113
    AgX
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    Farbenlehre...

    "The rays are not coloured", W.D. WRIGHT

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