American cinematographer (Jan-Dec 1927)

Ten AMERICAN C INE M A T O G R A P H E R May, 1927 Formula Safety base Nitrate base Ammonia (cone.).. 5 cc. Liquid slightly Same as Water 95 cc. colored in 10 safety Motor alcohol to. ...1000 cc. minutes. base. Ammonia (cone.).. 5 cc. No effect in Liquid Water 95 cc. 2 hours. slightly col Isopropyl a 1 c o h o 1 ored in 10 to 1000 cc. minutes. Ammonia (cone.).. 5 cc. Slight effect No effect in Water 95 cc. in 1 hour. 16 hours. Tertiary butyl alcohol to 1000 cc. The propensity of the cleaner to remove the tint varied with the different colored bases but the above table gives data for the base which was most readily attacked. Since the period of application of the cleaning liquid is very much shorter than that required to visibly affect the tinted case, the cleaners are considered satisfactory. 2. When making positive prints from negative film, the negative accumulates more or less dirt, grease, and loose particles of dust which must be removed at frequent intervals. In any case it is advisable to remove dust after every third or fourth passage through the printer by passing through silk plush (cut on the bias) moistened with a suitable cleaning liquid as the film is being wound on a rewinder. More thorough cleaning of the emulsion side can be effected by winding the film base side downward on a cloth-covered drum as above. The requirements of a suitable cleaning liquid for this purpose are similar to those for positive films dealt with below. 3. Positive film accumulates more or less dirt and oil during its passage through the projector, which causes spots and patchiness on the screen. In this connection film which has been toned has a greater tendency to show oil spots than untoned film, which is presumably a result of the matte surface produced by certain toning processes. The oil and dirt may be effectively removed from the film by immersing in a suitable oil solvent, with or without scrubbing, and then removing the excess solvent by squeegeeing and buffing. A satisfactory machine for this method of applying the solvent is by means of silk plush as the film is being wound on a rewinder. Various liquids have been suggested for the above purpose but the precise effect of such liquids on the film base and on the image, so far as is known to the author, has not been investigated. Moreover, in certain cases deterioration of the film image has been definitely traced to the use of unsuitable chemicals. An investigation to determine the most suitable liquids for the above purpose therefore seemed dsirable. Requirements of a Suitable Film Cleaning Liquid A suitable film cleaning liquid should possess the following properties : 1. It should readily dissolve fats and mineral oils. 2. It should not affect the gelatin coating or the film base, or remove the color from film with tinted base. Also it should not attack the silver image or a tinted or toned image even on prolonged contact in the presence of moisture, because when cleaning on a rewinder any excess of solvent which does not evaporate is trapped between the convolutions of the film, when it can evaporate only very slowly. It should also not decompose on exposure to light to give products which are injurious to the film. 3. The boiling point and latest heat of evaporation should be such as to permit of sufficiently rapid drying. 4. It should be non-combustible, non-toxic, and be readily available at a reasonable price. At the outset a survey was made of all the possible commercially available non-inflammable and inflammable oil solvents, and the most promising of these were investigated as follows : Non-inflammable Oil Solvents The following compounds were selected by virtue of their suitable volatility, solvent action, and price: Solvent Formula Boiling Point Dichlorethylene C2H2C12 56 60°C. Trichlorethylene C2HC13 85 87°C. Tetrachlorethylene C2C14 119-1 21 °C. Ethylene dichloride C2H4CL 83°C. Carbon tetrachloride CC14 76°C. The effect of these compounds on the film was investigated as follows: Effect of ~N on-Inflammable Solvents on Motion Picture Film The effect of the above solvents on film was studied by placing a strip of developed positive motion picture film (nitrate base) in a lOOcc. stoppered bottle with 40cc. of the solvent and 3cc. of water at room temperature. The film was thereby subjected both to the liquid and its vapors. Any tendency of the film to curl or of the image to change color was observed after 18 hours with the following results: Solvent Condition of Film (Nitrate 'base) after 18 hrs. at 70°F. Dichlorethylene (pure E. Slight curl when wet. Bad K. Co.) curl when dry. No effect on image. Trichlorethylene (Com. E. No effect on film base. EmulK. Co.) sion softened and image ob literated. Trichlorethylene (pure E. No effect on image or film K. Co.) base. Tetrachlorethylene (Dow) Slight curl when dry. No effect on image. Ethylene dichloride (pure Bad curl. No effect on E. K. Co.) image. Carbon tetrachloride No effect on base or emul(Dow) sion. Carbon tetrachloride (pure No effect on base of emulE. K. Co.) sion. Any curling tendency in the above tests was an indication that the film base had been attacked. The tests show that dichlorethylene and ethylene dichloride exert a sol(Continued on Page 20)