Journal of the Society of Motion Picture Engineers (1930-1949)

light is sufficient to give us the final results. This is because the working image is formed from that insignificant latent image by chemical reactions which themselves put energy into the system. In the case of diazotype, this is not the case, and all the energy needed to form the image must come from light energy. This is, of course, limited by the quanta of light available. In the case of the diazo system, which is a positive process, the light destroys the ability of the colorless dye precursor to couple to form the colored dye. Thus the areas receiving the most light, of course, give the least color on development, and those receiving no light give the densest color. But the energy necessary to make the change which produces the image is a result of energy applied to the system by the light, which makes the exposure. The chemical reactions taking place in the coupling reaction after exposure do not introduce chemical energy in the way that a silver photographic developer applies it. Diazo materials have been experimented with as print material for photographic uses,3 and even the simplicity of processing has not completely offset the low sensitivity and the short tone scale. Its success here has been in reproducing the sound track used in optical methods of sound recording.4 Its ability to produce high resolution has been given as a great advantage here. However, the newer magnetictape methods of sound recording appear to be better at the present state of our knowledge. As an example of what has been done with diazos, one fascinating attempt to improve this material, especially in its sensitivity, has been that worked out by the Philips organization of Holland and described in detail in the Journal.* Here, the low cost of the diazo material and its great resolving power are made use of, and the lack of sensitivity is partly overcome by combining with metal systems of mercury or cadmium, and by using silver and other materials in the "development." However, technical difficulties have yet to be completely overcome, and the process has not yet been put on the market. We will not take time here to discuss it in detail since it has already been well described in our Journal, as well as in other publications.4-5 A related system is that employing the diazo sulfonates,2-6 which differ from the diazo system in that they produce a negative-type image such as we are familiar with from silver salts. The other interesting aspect of these compounds is that some of them are developable by the application of heat,7 rather than by chemical reactions of separate developers. However, these compounds do not appear to be as sensitive even as the diazo compounds themselves, and there is great difficulty in trying to make papers or film materials with them which are stable enough to store or ship. Brief mention should be made here of the dye-bleach color systems,8 such as those used in such color photography methods as the early types of Caspar color and others, which have been amply described in our own Journal and corollary literature. Here again we have the difficulty of sufficient sensitivity for original taking-film, but the materials have been applicable to making prints from negatives produced by using other processes. Of course, several very old systems that have been used for reproduction purposes are those like the gelatindichromate9 system, or its cousins, wherein there is a differential hardening of a gelatin or other colloidal layer by the action of light, which affects the inkreceptivity of the layer.9* These systems are the mainstay of the printing trades today and they are exceedingly useful in many ways, but they have a low sensitivity and require arc-light exposures, as well as freshly coated material prepared just before exposure. Recent 60 July 1952 Journal of the SMPTE Vol.59