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

attempts have been made, some successfully, to utilize diazo-type compounds in printing-plate materials10 in order to obtain presensitized plates which can be prepared and stored for some time before use. These still, however, require strong light sources and long exposures. All these systems require the use of a "screen" in order to reproduce tones, which limits their usefulness. In somewhat the same field, fall the various differentially hardened plastics and resins,11 and the old methods utilizing such materials as bitumen and pitch. As a matter of fact, some of the very old photographic processes antedating the daguerreotype utilized such systems12; however, they required exposures to sunlight in terms of hours, and did not give a very stable result. An interesting variation of this idea is a recent report from a German experimenter13 of the fact that the use of a tanning developer such as catechol, on a silver halide emulsion in gelatin will produce shadow detail in the gelatin itself in areas beyond those which receive the weakest silver image upon development. It is proposed to make use of this by dying the gelatin and then washing away the unhardened lesser-exposed areas with warm water, leaving a silver image, together with this dye-plus-gelatin image, which combines to make a denser negative, especially in the very weak shadow regions. This would, of course, require a special type of emulsion and additional special treatment which, though it appears to be capable of greater sensitivity than the silver methods normally used, requires extra care and treatment in processing which makes it difficult of application. Salts of various heavy metals such as lead,14 thallium,15 selenium16 and many others have been used to form photographic images, such as were also formed in an experiment during the late war by one military man who used the familiar trinitrotoluene or TNT to make a photographic image.17 He did this by coating paper with a solution of TNT, drying it and exposing it to light. In all these cases the sensitivity so far appears to be very low, and no method of increasing the sensitivity has yet been reported. One rather surprising nonsilver system has recently been proposed which is brought to mind by the use just mentioned for TNT. This is the use of explosive materials to form an image by the results of the explosion. In a recent report the use of nitrogen triiodide is described. This is a ticklish material which many of us used to use in schooldays for practical jokes; it will explode with great noise when slightly disturbed, even when tickled with a feather. In this case, the light falling on it through a lens is sufficient to set off an explosion, and an image is left on the support, burned in by the explosion. 18 The light-sensitive glasses developed by the Corning Glass Works19 are of interest, especially as they will give some colors as well as black-and-white images, but they are not practical for motion picture engineering use because of the fragility of the base material, the special processing (requiring very high temperature fusing) and other difficulties, which we understand also include a low sensitivity. The colors obtained are not "natural" colors as in Kodachrome, etc. On the other hand, quite interesting advances have been made with various processes of electro-photography, such as have been developed at the Battelle Memorial Institute in connection with the work of Haloid Go. under the name of Xerography.20 Further work on this has been done at the Signal Corps Engineering Laboratories (Squier Signal Corps Laboratory) at Fort Monmouth, N. J., and reported in the recent literature.21 They appear to have overcome the early difficulties of poor tone-scale Thomas T. Hill: Nonsilver Photographic Processes 61