The Educational screen (c1922-c1956])

Page 20 The Educational Screen FILM PRODUCTION IN EDUCATIONAL FIELD THE Conducted by F. W. Davis Department of Photography Ohio State University, Columbus Storage and Preservation of Film /~kNE PHASE of the motion picture activity which ^-^ has been neglected by the average amateur is that of storage and preservation of iihn material. It so often happens that a school will procure a fine film, en- tailing considerable time and expense, only to find that a few years later the film is in such condition that it cannot be shown and is worthless. All motion picture films and film strips are produced on either cellulose acetate (slow burning, safety film) or cellulose nitrate (inflammable) stock. All 16 mm. films in this country are produced on acetate base, while the 35 mm. is produced on both. Almost all of the Hollywood professional films are made on the inflam- mable nitrate stock although many of the present day 35 mm. teaching films are coated on the safety base. This means that, first of all, one should ascertain which type of film is being used and especially which type of film is being stored in the film vaults or cabi- nets. Nitrate film should be used as little as possible as the danger with this type of film is due mainly to its rapid burning rate, its ability to burn in a limited supply of air and its low temperature of ignition and combustion. Most substances, such as wood and paper, do not ignite until a temperature of around 600° or 700° F is reached, while nitrate film will decompose at 230° F or at the temperature of an ordinary incandes- cent bulb or steam pipe. *^) There is very little danger in free burning nitrate film is the open air, but on confining the com- bustion to a vault or film storage cabinet in a limited supply of air this burning film gives off carbon monox- ide, nitrogen dioxide and nitrogen tetroxide, all very dangerous gases. The fire hazard on acetate film is somewhat less than that of ordinary paper. The ignition temperature of this type of film is about 700° or 800° F. so that it is readily apparent that where films are shown to school children the safest type of film to use is cellulose acetate. It is hoped that no school will have the fire situation arise but if it does we should know what to do. Many of the present-day fire extinguishers are useless on a film fire and pails of sand to throw on the fire are likewise worthless. Water seems to be the cheapest and most eiTective method of combating a film fire especially when it is in the form of an automatic <1) Journal Society of Motion Picture Engineers Vol. XXVII No. 6, p. 657, A. H. Nuckolls and A. F. Matson. sprinkler. <^' It is much easier however, to practice fire prevention than fire extinction. Aside from destruction by fire a film may be de- stroyed just as "effectively" (although not so rapidly) as far as projection is concerned by storing it at an improper temperature or humidity. The present day "safety" film tends to curl and become very brittle when dry, whereas the nitrate film has less tendency towards these conditions. Everyone who has used 16 mm. films has noticed at some time or other that they become extremely brittle with Icng periods of storage. It has been found *'* that at a relative humidity of 15% or the condition in an average home during the winter months, the films are extremely brittle and will either not project at all or trouble will be encountered during projection. A relative humidity of 50% is found to be ideal for storage of films. This, incidentally, is the condition that has been found best for books in libraries. One must not go to the other extreme, however, and keep films in an atmosphere which contains too much water vapor, otherwise condensation will take place and be just as detrimental as a dry condition. How then are we to keep films at the right humid- ity? In the majority of cases an individual would be unable to maintain the 50% condition but, by all means, try to approach as nearly as possible to this ideal. Very little trouble will be experienced in the summer months as the humidity is normally satisfactory at that time. Films should be placed in individual metal con- tainers which contain an absorptive pad, which if kept continuously moist will retain the films in good condi- tion. If many such cans are to be stored for any period of time it is desirable to place them all in a large con- tainer which also contains a large humidifying device. Safety film which has become brittle may be re- stored to its original condition by replacing the mois- ture content, although this is sometimes a long pro- cess and may require several weeks. However, by running the film through special chambers or pads made for the purpose of rehumidification, films may be brought back to their original condition in 10 to 30 minutes depending upon their dryness. Temperature is also a factor in film storage although not so important as humidity. Possibly the ideal tem- (2) Journal Society of Motion Picture Engineers Vol. XXVII No. 6, p. 662, Henry Anderson. W Journal Society of Motion Picture Engineers Vol. XXVII No. 6, p. 694, Weber and Hill.