British Kinematography (1949)

15 The new safety base is less readily attacked by the solvents used in film cements, and therefore it is the more important that the cement be given full access to the base by complete removal of the clear gelatin sub-coat, which lies beneath the emulsion. Of course, if the splice is properly scraped, this factor will automatically be taken care of. Slight roughening of the base on the other half of the splice also assists in ensuring a good weld. IV. CONCLUSION To summarise, we appear to have in this new safety film base a material much improved in comparison with earlier safety types, and which compares well with nitrate in most mechanical qualities, although still not quite so good. But against the slight disadvantages account must be taken of the film's slow burning qualities, the better retention of mechanical and chemical characteristics under severe aging tests, and its exceptionally low permanent shrinkage. We may well hope that following the introduction of this new base, safety film will soon establish itself as the standard material for all forms of professional motion picture work. The information contained in the above paper is based on data supplied by the Eastman Kodak Company in the United States, and especially on a paper by Dr. C. R. Fordyce recently presented before the Society of Motion Picture Engineers. DISCUSSION Mr. L. Knopp : In 1939, the Secretary of The Author : It is intended that this State set up a Royal Commission under new material shall eventually be used for Lord Stonehaven to enquire whether the old all types of motion picture film, safety film could be regarded as inflammable Mr. Brown : What is embossing ? Can within the meaning of the Cinematograph Act and the Celluloid and Cinematograph Films Act. In its report, the Royal Commission stated that in its view the then slowburning film was outside the scope of the Cinematograph Act. This new safetyfilm has slow-burning characteristics far superior to that of the early kind. A curious position is likely to arise when the kinematograph industry uses this new film base exclusively, because as the law now stands, licences will not be required. I doubt, however, whether this position would obtain for very long because there are many considerations of public safety which are far removed from the use of inflammable film. Mr. H. S. Hind : Have any laboratory life tests been carried out, using slightly differently designed sprockets ? The Author : In the U.S. the diameter of the standard intermittent sprocket has been changed in view of the lower shrinkage characteristics of the material. The previous diameter of 0.935 in. was in 1947 modified to 0.943 in. and incorporated as an American Standard. The earlier sprocket was calculated on the assumption of a 1.2% film shrinkage, which was very high. Mr. B. C. Sewell : Will the new film base be used for all types of negative material ? you say something about the relative transparency of the two bases ? The Author : Embossing refers to a deformation of the base which appears as a local curl, and is due to differential heat absorption by the film according to its density. Frame line embossing has little influence on picture quality, but can interfere with reproduction of the sound ; image embossing affects the focus of the picture. There is no difference in the transparency of the base of safety and nitrate films. Mr. Sewell : On the question of hardness of the film, has it a tendency towards scratching ? The Author : Scratching qualities are associated with tensile strength and elasticity, which on the safety base is a little inferior to nitrate, so there may be a very slightly greater tendency towards scratching of this base, although on practical tests this has not been observed. Mr. N. Leevers : What happens when you join ordinary safety film and nitrate base? The Author : Safety cement will serve for joining safety and nitrate bases, but in America an alternative cement is employed which incorporates solvents specially suited to the new safety base. Tests are still going on to find the best formula. [Continued overleaf