American cinematographer (Jan-Dec 1924)

November, 1924 AMERICAN CINEMATOGRAPHER Twenty-three perature of the various solutions should be maintained as nearly constant as possible, that is, the temperature of all the solutions should be equal because if a swollen film is subjected to a sudden change of temperature, for example, if it is removed from a hot solution to a cold one and vice versa, the gelatine film is subjected to strain and a leather-like graininess of more or less coarseness will appear all over the film which effect is known as reticulation. Recent experiments have shown that excessive graininess of film finished in hot weather is a mild form of reticulation. The effect of a sudden change of temperature is at maximum when the film is excessively swollen and a minimum when unswollen and hardened. Several procedures are, therefore, possible, as follows: A. Maintain the temperature of all solutions equal to that of the wash water. B. Use a cool developer and warm hardener, fixing bath, and wash water. C. Use a cool developer and hardener and warm fixing bath and wash water. All the above give good results though C is the best procedure if cooling is possible. The wash water may be either hot or cold, that is, once the film is tanned in the unswollen condition it will withstand sudden and severe changes of temperature without reticulating. The usual difficulty encountered when drying film at high temperatures when high humidities usually prevail is a result of excessive swelling of the gelatine which, therefore, contains an excessive quantity of water. If swelling of the film is prevented by the above recommended procedure, drying will be rapid and can be hastened by raising the temperature of the drying air which in turn raises the relative humidity without danger of softening the film emulsion. Rapid changing of the air in contact with the film surface is also of importance. In the field, a mosquito netting cabinet is necessary to prevent access of insects to the film. Excessive graininess of the film which is often produced by slow drying at high temperatures of excessively swollen film, does not occur if swelling of the gelatine is prevented as explained above. Experiments have shown that the wearing qualities of film processed in the above manner are not materially affected as a result of the excessive hardening with chrome alum. If the gelatine coating, however, is excessively swollen at any period and especially before hardening, the structure of the finally dried hardened gelatine is more or less spongy and it has, therefore, much less strength than gelatine which has not been swollen. Suitable apparatus for handling motion picture films in the field at high temperatures has been described in previous papers4. At normal temperatures film undergoes only a very slight change with age — so slow that no alteration of its physicial properties takes place for several years, providing the film is not allowed to become excessively dry. Under certain conditions, however, the film base undergoes actual chemical decomposition, depending on the conditions of processing and storing. It has been found that small traces of impurities in the gelatine film such as residual chemicals left in the film either as the result of imperfect fixing or the use of an exhausted fixing bath, or as a result of imperfect washing, or thorough washing in impure water, very materially hastens the decomposition. Film which is to be kept for 4. "A Portable Apparatus for Developing M. P. Film at High Temperatures," by J. I. Crabtree. B. J. Phot. Aug., 1918, 379. "The Development of M. P. Film by the Reel and Tank Systems," by J. I. Crabtree, Trans. Soc. M. P. Eng. Vol. 16, 163. any considerable length of time should, therefore, be thoroughly fixed in two successive fixing baths and thoroughly washed in pure water. Experience has also shown that even film which has been thoroughly fixed and washed when stored at high temperatures rapidly becomes brittle, the film base undergoes chemical decomposition, and in a few years' time the film image is destroyed by the decomposition products. At normal temperatures the rate of decomposition is negligible, but with rising temperature above 80°F. decomposition takes place at a very rapidly increasing rate. It is very important, therefore, that film should be stored at a temperature not higher than 60 to 70°F., though a temperature around 40 to 50°F. is to be preferred. IMPROVEMENTS IN CINEMA LABORATORY APPARATUS (Continued from page 7) means of springs so that the film is maintained as nearly flat as possible. Transparency titles are illuminated by means of a bank of "Cooper-Hewitt" lamps placed behind the frame (F) while reflection titles are illuminated by a bank of lights placed on each side of the title card holder. The apparatus was originally fitted with a bank of nitrogen filled lamps arranged in the form of a square immediately in front of frame (F) but when photographing on positive film the photographic actinic power of such lamps is very much lower than that of mercury vapor lamps so that this method of illumination was abandoned. When making titles by reflected light, the frame (F) is removed by inscrewing clamps (P'P2) and a wooden board to which the cards are pinned is then attached to the aluminum plate by means of thumb screws. It is apparent from the above that when operating, all adjustments can be made while viewing the title image in the camera gate. In order to insure that the printed matter is paralled with the frame line, it has been found most convenient to sight across a straight edge fitted to the top of the camera. In this way strict parallelism is insured even though the camera itself may not be level. 2. A Continuous Film Viewing Machine This machine was constructed in order to permit of viewing the continuity of negative and positive film and for cutting out defects at the assembly table. It has been found most useful for examining negative film but for small laboratories it should prove useful for the final examination of positive film without the necessity of examination in the standard projector. In the larger laboratories a continuous projection machine would appear desirable because it would be less liable to injure the perforations at the high projection speed employed in many inspection rooms. It is impossible to project film at three or four times the normal rate of projection in an intermittent projector without producing corner fractures or otherwise injuring the perforations unless the projector mechanism is examined at very frequent intervals. It is important that more care in projection should be taken on the part of laboratories in order to insure that the wearing qualities of the film are not impaired when it leaves the laboratory. By means of a single sprocket the film is drawn continuously and without intermittency past an aperture plate fitted with a viewing eye-piece and at the point when each picture frame registers with the aperture or gate it is instantaneously illuminated so that an intermittent effect