American cinematographer (Jan-Dec 1926)

July, 1926 AMERICAN CINE M ATOGR APHER Thirteen PIG S Bleaching Effect of Reo Light on Desensitized Film MOTION PICTURE MCG*rrvc Fll_M | oeseNsrriEEo emim in pmaKR-n-OL meen zooo EXPOSED 1 WCM (E CNl)PROM 3ER I SAPELIGHT I NO EXPOSURE BCPORE OEvGLOPNIENT 3 . IOMIN< . (LOO E ) DENSITIES OP STEP TABLET I I 4 ,*£ EffectofaPreliminaryBathon Rate *«> ' of X>^ «$>•"*!« E Development and Fog Time op ocvtuopipENT exposed to a Series 1 safelight at 1 inch for 5 and 10 minutes and the several parts of the sheet developed together. The progressive destruction of the lower densities and resulting increase in contrast are evident. Of course these conditions are much more severe than would occur in practice. In Table III the results of another interesting experiment are tabulated. A sheet of motion picture negative film was given a flash exposure sufficient to develop to a density of about 0.90. It was then cut into strips which were desensitized for 5 minutes in solutions of pinakryptol green of the various concentrations given. Parts of the wet strips were then exposed one inch (2.5 cm.) from a Ser. 1 safelight for 2, 5, and 10 minutes and all developed. The resulting densities show that when the treatment was sufficient to prevent fog, bleaching occurred. Under these conditions with a concentration of 1-1,000,000 the film increased in density, while with 1-100,000 the latent image was bleached. When a Series 0 safelight was used the change took place between 1-100,000 and 1-50,000. Table 77/ Effect of Red Light on the Density of Pre-exposed Film. Desensitized for 5 minutes with Different Concentrations of Pinakryptol Green Concentration Time of Exposure to Red Light. None. 2 min. 5 min. 10 min. 0.92 0.99 1.19 1.55 No. 1 2 3 4 5 of Pinakryptol Green. None 1-10,000,000 1-1,000,000 1-100,000 1-50,000 0.91 0.89 0.88 0.89 0.98 0.98 0.76 0.82 1.15 1.12 0.47 0.45 1.40 1.26 0.24 0.19 In the case of a developing paper which showed bad abrasion it may be of interest to note that when bathed in pinakryptol green and exposed to red light a latent light image was destroyed without affecting the abrasion. Carroll6 found that pinakryptol green destroyed a latent image on process plates • in the dark in a few hours. A test on motion picture negative film showed that after a week the latent image of a step tablet exposure was appreciably diminished. After three months it was again tested and found to have nearly the same threshold exposure but the contrast was much less. With fine grained emulsions the bleaching would no doubt take place much more rapidly. We may conclude, therefore, that it would not be safe to desensitize exposed negatives and then keep them for any considerable length of time before development. 4. Fog Produced by Pinakryptol Green in a Preliminary Bath. Many dyes which have a strong desensitizing action are such bad fogging agents that they cannot be used for this purpose. Pinakryptol green has some fogging action and this fact must be considered when using it. The intensity of fog produced as well as the effect on the speed of development varies greatly with different developers. In order to find something of the extent of such variations, strips of motion picture negative film exposed uniformly along one edge were dipped into a solution of pinakryptol green 1-10,000 for 5 minutes, wiped with a chamois, and lowered into a tube of developer at regular intervals so that a range of development times was obtained on the same strip. Comparison strips were made by soaking in water instead of desensitizing. The densities of the image and fog were then plotted against time of development. Typical curves for three different developers are shown in Fig. 9. With pyro 1:1 (B. J. formula) the fog on the desensitized strip was enormously increased, and although the first appearance of the image was accelerated its later development was greatly retarded. Dilution of the pyro 1:1:2 did not change appreciably the retarding or fogging action for a given degree of development. With chlorhydroquinone the fog was somewhat increased for a given time, but the initial accelerating action on development was so great that it extended throughout any ordinary development time. With glycin no fogging action occurred, the image appeared sooner on the desensitized strip but the growth of density on prolonged development was retarded. From these curves it is evident that pinakryptol green in a preliminary bath affects fog and rate of development very differently with different developers, and whether it retards or accelerates development depends on the particular point at which a comparison is made. These facts show why conflicting statements on this subject might easily occur in the literature. It should also be mentioned that a desensitizing bath which has been standing for some time in a tank may accumulate a scum on the surface which must be removed before using or it will stick to the surface of a film causing a bad smeary fog. (Continued on Page 20)