British Kinematography (1952)

May, 1952 brown: problems of storing film 157 that the Library was first brought up against this problem of films becoming sticky, when one of our films was found in this state. Very shortly after, Mr. C. Smith, of Kodak Research Department, devised an artificial ageing test using litmus as an indicator.7 In 1946 we started using the present test, identical in principle,3 but further developed by Mr. S. A. Ashmore, of the Government Laboratory, and a member of our Technical Committee. The test depends upon the controlled acceleration of the decomposition by application of heat, A disc of film \ inch in diameter is punched out of the reel and dropped into the bottom of a small test tube. The top of the tube is then closed with a glass stopper, round which is wrapped a piece of filter paper, impregnated with an indicator dye, Alizarin Red, and moistened with glycerine and water. The stopper and paper make a close sliding fit in the test tube; and the tube is then heated in an air bath at a temperature of 134° C. The upper part of the tubes protrude from the top of the bath and are continuously visible. The time required for the development of acid vapours is revealed by bleaching of the lower edge of the paper. The tubes are watched for sixty minutes and the result is recorded as the number of minutes required for the colour change to occur (Fig 7). It has not yet been found possible to relate precisely the number of minutes recorded as the result of this test, to a certain number of years of remaining life. There probably does not exist any precise relationship, but the results are a reliable guide to a certain minimum remaining life. Thus any film which at the end of sixty minutes gives no result, may safely be left for three years. At the end of this time, it is tested again. If the result is between forty and sixty minutes, the film is tested again after twelve months. If between twenty and forty minutes, after six months. Any film giving a test result under twenty minutes is regarded as unstable, since it is at this point that it becomes increasingly acid and is liable to become sticky. Fig. 6. Showing construction of draw in experimental store. When we commenced to test all the films of the silent era we found 9 per cent, of those tested in the first year were unstable. As we have weeded out the existing unstable films, this proportion has dropped, until during 1951, when 1,700 tests were carried out on 1,143 films, only 5.6 per cent, of the films were found unstable. Without this test, the storage of films would be useless, since only by its agency are we able to anticipate the ruin of the film. Upon any film being found unstable, if the subject matter which it contains justifies its continued preservation, it is copied before it reaches the state in which copying is impossible. The Library has three Selection Committees whose responsibility it is, to decide in each case, whether or not a film shall be duplicated. Since the inception of this testing programme, 448 films have been duplicated, which otherwise would have been lost. Questions of Duping. The making of dupes is a normal laboratory practice and we are told that it is possible to duplicate an original negative with practically no discernable losses, but this applies of course to normal current work. The physical condition and photographic quality of most of the old films in the National Film Library present additional and different problems. Although it