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

reproduction, and we have seen portraits made by this process which had fairly good quality. The process basically involves the "sensitizing" of a prepared selenium plate by giving it an electrostatic charge. Upon exposure to light, in our case to an image, the resistance of the plate drops in the higher exposure regions, so that the charge there is less. Development consists of dusting on a dry powder which clings to the areas still holding the most electrostatic charge. This powder image may be fused to permanence by heat, or transferred to another paper support and then fused. Three to five seconds in a photographic dry mounting press will do the trick. The plate itself can then be cleaned and re-used for another picture. The great advantage here is the speed of processing and the fact that it is an all-dry system without water solutions. However, the manipulation by the operator including the preparation of the plate just before exposure, whether of selenium or of phosphors22 (both of which systems are used), is quite difficult and delicate, and a high-tension electrical system is necessary to utilize this method. It gives a direct-positive result, and does not as yet appear to be applicable to a negative-to-positive system. However, a great deal of work is being done on it for the various applications such as photocopy work, special Air Corps cameras, and even for X-ray use,23 and to prepare lithographic printing plates.24 Another interesting process announced fairly recently, is that referred to as thermography,26 exemplified by the heat copying process, recently announced by the Minnesota Mining & Mfg. Co. In this process, called Thermofax, the image is formed by an infrared or heat exposure which melts a waxy material where inked areas concentrate the heat, and the resulting image on a special paper is both a positive and a negative. This may be rather confusing, but the fact is that as a result of this exposure you get a print on a semi-opaque paper which by reflected light looks like a positive, since the exposed areas are darker than the chalky blue-white background (of the example we saw). However, when viewed by transmitted light, those exposed areas become a transparent light blue against an opaque whitish-blue background, and form a negative image which can be used to make prints by usual contact printing methods on silver-salt materials. This appears to have interesting applications for office photocopy use, and this is the first commercial application being worked on. However, it requires exposure to heat, or infrared rather than visible light rays. It does not appear to have a great deal of tone range, and it appears to be very slow, as with so many of these nonsilver systems; therefore, as presently described, it does not appear to have any application at all for our present purposes. Conclusions Having now discussed and described some of these proposed light-sensitive systems, the question is, Where do we go from here? It would seem that each of these systems, which we have so briefly examined, has at least one great shortcoming in comparison to the silversalt process we are so familiar with. They all appear to have a low sensitivity to light. Many of them appear to have a poor tone range, and some of them seem to require even more complicated processing techniques to produce the final image. It would therefore seem that, as presently developed, none of these systems has any immediate direct application to motion picture photography, that is in preparing either the positive print or the negative film from which the positive is printed. There are a few cases, such as the Philips diazonium system, which appear to have some promise for making prints. This is also true of 62 July 1952 Journal of the SMPTE Vol. 59