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

diazo dyestuffs; diazo sulfonates; metaldiazonium system; dye bleach color systems; gelatin dichromate systems (and similar ones used in the graphic arts); thermography (such as the Minnesota Mining system); light-sensitive glasses (such as those of Corning); differentially hardened plastics and resins (such as bitumen, etc.); miscellaneous metals and metal salts (including those of lead, thallium, selenium, etc.); iron (such as those in blueprints); electrophotography (such as Xerography); platinum and palladium compounds (actually used in making prints from silver-salt negatives) ; and mercury salts. Some of these processes or systems appeal to us because of either simplified processing, adaptability to varied temperatures, low costs or great stability in the final product. But, when balanced against the advantages of the silver process, they have all, up to now, fallen short, except for single specialized uses. It is that aspect which will be discussed here in some detail. We should know something of what we can expect from these "new" systems and what we should not expect from them. In some cases, enthusiasm has been substituted for results, and we have to use some caution in assessing the reported examples of new proposals. Evaluation of various systems: Of course, not all of these nonsilver systems are new; many of them have been used for years for specific purposes. One of the most used is that based on the light-sensitivity of iron compounds which form a blue-colored salt upon exposure to light. We are all familiar with the blueprint, and many of us have used blueprint paper to make prints from still-camera negatives. The process, as you will recall, is very slow, requiring strong artificial light, or sunlight, and in most cases the papers in use are designed for high contrast rather than for continuous tone reproduction. As generally used, the results are not as permanent as silver images, although with proper treatment they can be made quite satisfactory.1 But such special treatment eliminates two of the blueprint's advantages, low cost and simple processing. On these bases, together with the low sensitivity, we can eliminate this system from our consideration as a possible competitor to a silver compound in actual motion picture work. In the field of plans and engineering drawings, the diazo print2 is replacing the blueprint since it is a positive method, giving a positive copy of the original, and having greater contrast. Properly prepared, it is also more stable. Because of its ease and cheapness of processing and the low cost of the original material, the diazo system of photography is more promising than many others, and much effort has been put into it to make it more useful, and more of a competitor to the silver system. However, it has some important disadvantages from our present viewpoint, mainly very low sensitivity and a limited tone range. For black-and-white photography, the diazo system has another disadvantage in that there is no true dense opaque black available. The best blacks, so far, in this field are mixtures of dyes giving a very dark color which appears black on an opaquebase print, but does not have the density of a silver material. The low sensitivity here is the problem which we meet again and again in studying the various nonsilver systems. In general, the advantage of the silver system is that it can be sensitized (in the meaning of that word used by emulsion chemists). That is, by adding small amounts of certain dyes and organic compounds together with sulfur compounds, the sensitivity of silver salts to light, including now the use of fluorescent materials, is greatly increased. But there is another great difference. In silver photography, a latent image produced by a very small amount of Thomas T. Hill: Nonsilver Photographic Processes 59