Principles of cinematography : a handbook of motion picture technology (1953)

PROCESSING MOTION PICTURE FILM 107 of this, a film bearing an even exposure throughout its length may have a heavier density at its leading edge than at the trailing edge. The effect is most marked with films containing very contrasty subjects, such as the example shown, since the developer which comes into immediate contact with the film is carried downwards with it to some extent. That is to say, the film is not able to cut a clean path through the developer, but must drag some of the solution along with it. The ability to develop neighbouring areas to an equal extent will therefore depend upon the amount of work the solution is required to perform. In the example, the number has been fully developed out and such development has left the solution temporarily exhausted over this region and, therefore, reduced its ability to develop the background immediately following that number. Directional effect may be reduced by increasing the rate of developer circulation, avoiding any film path in the horizontal direction, maintaining fresh solutions and, should it be necessary, introducing stationary rubber squeegees at points throughout the bath to mechanically wipe away the exhausted solutions although fortunately, this last preventative will only need to be used in very rare and severe cases. drying troubles. If the film is dried too rapidly or excessively it will not contain sufficient moisture to maintain a flexible condition and will become brittle. This condition may cause the film to roll up on the take-up core in a very irregular manner and tend to form itself into a hexagonal shape. If, on the other hand, the film is dried in an atmosphere of high humidity, it will be rolled up very freely but, on coming into contact with normal humidities of other rooms and whilst still in the rolled state, it may become buckled along its length. This occurs because the moisture contained in the film is only able to escape from the edges of the roll and, consequently, the centre of the film (viewed along its length) remains at a higher relative humidity and will therefore tend to maintain a greater length than the edges of the roll. failure to harden. This may be due to excess acid or sulphite content in the fixing solution, to a low alum content or to the use of wrongly compounded alum. Under such conditions the amount of alum, acid and sulphite in the solution should be carefully checked. ftxer scum. This is usually produced when the fixer is somewhat exhausted and has not been used for some days; under such conditions the hydrogen sulphide in the atmosphere reacts with the silver thiosulphate in the solution and produces a metallic-like surface scum on the liquid. The scum should be drawn off the surface of the solution before it is again fit for use. fker stain. The precipitation of sulphur on the gelatin will produce a yellowish stain and indicates that the fixer has not been correctly made up is usually too acid or lacking in sulphite. Similar results are produced when the fixer is operated at a temperature considerably above normal. fogging. (General Notes). As most people are aware, 'fogging' is a term used to describe any density which appears in the developed film and is not a direct result of intentional exposure. Any photographic emulsion will tend to fog if it is kept for a considerable time before use