Movie Makers (Jan-Dec 1930)

J7%.imiajy«.ic'»' 1950 HOME LABORATORY WORK An Outline Oj The Why And How Of This Interesting Activity By Herbert C. McKay WITH the growing interest in amateur motion picture photography, there is a corresponding growth of interest in the technical phases involved. Among the subjects which are occupying the minds of many amateurs, the home processing of films is not the least in importance. This is not due to any difficulty in securing adequate service from of the theory of development will be all that is necessary. Development, or more properly speaking, film processing, involves five distinct and important steps — development, fixing, washing, drying and polishing. These steps, which carry the film from the camera to the printing machine or projector, will be discussed in their proper turn. routine motion picture work are glycin, metol and hydroquinone. Of course, it is obviously essential that the silver bromide be changed to metallic silver in proportion to the amount of light allowed to fall upon it. In no other way would it be possible to secure a delicately graded photographic image. If the exposed film were to be placed into a solution of the reducing agent alone, we would find that the reduction would fail to be proportionate to the amount of light received by the film, as a certain amount of the silver bromide which had not received any light would also be reduced. This would give to the film a general gray tone which we ordinarily speak of as the laboratories, as both reversal and negative-positive processing is done quickly and satisfactorily by many of them. The interest lies rather in the fact that amateur motion picture photography frequently appeals to a class of enthusiast who likes very much to perform every step himself. In addition to this class there are also some investigators and experimenters who make shots which they should not like to have disclosed until they see the film screened for themselves. It is to be hoped that all of those who, for one reason or another, are interested in home development will find in the following an answer to many of their problems. Above all else, it must be borne in mind that the development of the photographic image, whether in motion or still photography, is in itself a simple procedure which involves only a nominal expenditure of time and money. Theory oj Development. Practical men and particularly those who are seeking quick and easy results do not favor theoretical discussions. However, as it is almost inevitable that the beginner will encounter certain difficulties in the art of photographic development, a sufficient understanding of its theory is necessary. While photographic development is a simple procedure, it involves, at the same time, one of the most complex chemical reactions in common use. It is, therefore, fortunate that a complete familiarity with the chemical reactions involved is not essential to the proper use of the process. Thus, a superficial discussion 2i Development. Photographic development consists of a practical application of an apparently simple chemical reaction, namely, the reduction of metallic silver from its halide. Photographic plates and films consist of a suitable base upon which is coated a very thin layer of ordinary gelatin. Mixed in this gelatin, before spreading upon the surface of the support, is a substance which is sensitive to the action of very minute quantities of light. The actual substance in most common use today is silver bromide. When silver bromide, suspended in gelatin, is exposed to the light, a change takes place within the microscopic grains, which has not yet been fully explained. The change which takes place makes it very easy to break down the silver bromide, giving us in its place metallic silver. The change is effected through placing the exposed film into a solution containing a reducing agent. While reducing agents are ordinarily thought of as attracting oxygen only, it is well-known that the halogens — iodine, bromine, chlorine and fluorine — react with reducers just as oxygen does. The reducers commonly used are more familiarly known by certain trade names than by their true chemical names. Thus we are all familiar with the names metol, hydroquinone, pyro, amidol, glycin and others. Of these the most valuable in fog. We would also find that a film placed into a solution of this kind would have its silver reduced very slowly. Too, the solution itself, being composed of an active reducer, would absorb oxygen from the air and very rapidly become discolored, ultimately staining the; film. It is, therefore, necessary to add to the solution something which will increase the rapidity of its action, something which will prevent its deterioration through absorbing oxygen from the air and something to prevent the reduction of the silver bromide which has not been exposed to light. If we add to our solution some caustic alkali, such as sodium carbonate, this caustic starts a slight disintegration of the gelatin, making possible a much more rapid and complete penetration by the solution. As this facilitates the process of reduction it is known as the accelerator. Even with this addition we find the developer still darkens through exposure to air. If we next add to the solution some sodium sulphite, we can prevent this trouble. The action of the sulphite is a subject of some discussion but it is usually conceded that the sulphite is more readily oxidized than the reducer, although some chemists hold