American cinematographer (Jan-Oct 1925)

Tiventy-four AMERICAN CINEMA TOGRAPHER January, 1925 on film which had been refrigerated previous to humidification. The order of exposure appears to have little influence on the extent of the markings. 10. Serrated Edged Spots. — When film is subjected to abnormal humidity conditions so that the condensed moisture is sufricent to render the gelatine mobile, certain specific markings are produced on refrigeration. The most common spot has sharply defined edges deeply serrated with a slightly lighter density just inside the serrations, while the centre of the spot has a density similar to the remainder of the film. When conditions are reversed— that is, refrigeration preliminary to humidification, especially if the refrigeration is short compared with the time, in the humidor — the spots are likewise formed. A few examples were noted on film treated at tropical temperatures, which was exposed after the moisture treatment. The order of exposing the film had only a slight effect on the tendency for the spots to occur. Miscellaneous Markings. — A few scattered examples of spots similar to Nos. 2 and 3 were noted. These were found chiefly on film which had been exposed and humidified at 110° F. for 48 hours and then refrigerated 24 hours, and in another case where the film had been refrigerated 48 hours and then humidified at 110° F. for one week. In one case where the film had been humidified at 110° F. for 24 hours and subsequently refrigerated 24 hours, there were a great many markings like No. 4. Generally speaking, there were very few examples of markings like those found where actual water comes in contact with the film as mentioned in under A, with the exception of the white spots (No. 1), which is the most common moisture spot observed on motion picture emulsions. C. Markings Caused by Abnormal Drying Conditions. Although drying marks are always produced on the emulsion side of film, their formation may be the result of either one or both of the following causes: (a) excess water remaining on the emulsion side of the film (as illustrated in figs. 11, 12, 13 and 14), or (b) excess water left on the base side of the film (as shown in fig. 15). In the latter case the local areas on the emulsion directly opposite the moisture spots on the base side, are cooler than the surrounding film, resulting in a selective drying action, as noted in a recent article by one of the authors.3 The severity of the markings produced by either of the above causes is directly dependent on the temperature and the humidity conditions and on the time of drying. 11. Spots with Dark Narrow Outlines. — This marking is distinguished by a dark narrow band, which constitutes the edge of the spot. All the area within this band is of the same density as the rest of the film. It is caused by large droplets of water remaining on the emulsion side. 12. Dark Grey Spots with Small White Centres. — When large drops of water are accidentally left on the film which is subjected to rapid drying at high temperatures (90-120° F.), spots are produced whose general density is considerably darker than the surrounding film. The point in the spot where the last water evaporates appears as a tiny white spot. In some cases, a narrow white halo may be found just inside the outer edge of the spot. 13. Hazy White Spots. — Occasionally on film which has been developed in solutions at temperatures around 80 deg. F. or over, when the gelatine is in a swollen condition, small vaguely defined white or grey spots are found, especially if the film is dried rapidly at high temperatures (120 deg F.), even when all superfluous moisture is removed. The markings resemble No. 1, except that the outlines are usually less clearly defined. 14. Streaks. — Sometimes streaks remain on the film during drying which causes long string-like grey marks of slightly heavier density than the rest of the film. Variations are found where edges are dark and the side of the streak slight grey. This marking occurs on film dried either at room or tropical temperatures. 15. Spots with Grey Halos. — The most common marking found as a result of the presence of water on the base side of film is a spot with a hazily defined edge or halo of much lighter density than the centre, where the densitv is nearly the same as the remainder of the film. On film dried at room temperature, this marking is just discernible, but at higher drying temperatures the spots are greatly accentuated. Other varieties are : (1) grey streaks along the edge of the film just inside the perforations as shown in fig. 15, and (2) small round light gray spots even density. All spots caused by water on the base 3. Crabtree, J. I., Trans. Soc. M. P. Eng., No. 16, p. 163 (1923).