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1950 SYNTHETIC COLOR-FORMING BINDERS 469
posure is safe with an illumination of 0.02 ft-c. While this is not quite as bright as safelights commonly used with black-and-white positive, it is very bright indeed for a film having essentially panchromatic sensitivity.
It is interesting to note in passing that a monochromatic source emitting the wavelength of one of the gaps in sensitivity would make a very efficient safelight indeed. Although the "D" lines from a sodium arc do not fall quite at an ideal wavelength, they do produce very high illumination for a given* level of "safety."
Printing Equipment and Illumination Requirements
A registration printer, either optical or contact, is required for exposing the picture images onto Type 275, because this operation involves three successive printings from separation negatives. Any conventional printer of this class may be used; the only additional specification over black-and-white printing is that filters must be placed between the light source and film.
Any standard light-change device may be used. These include traveling mattes, apertures, and lamp voltage control. It should be noted in the latter connection that perfect freedom is permissible in varying lamp voltage. Since the exposures are made through narrowpass filters, this process does not require that the source be operated at a fixed color temperature. Whatever the mechanism, it is desirable to have fine printer-point steps to give maximum control over color balance.
Regarding illumination requirements in the printer: a 500-w incandescent lamp 10 in. from the film plane, with spherical mirror, in a contact printer with Jfo~sec exposure time gives ample exposure.
PROCESSING Du PONT TYPE 275 COLOR FILM
Processing of Du Pont Type 275 Color Film consists of four chemical treatments, with water washes or rinses between. The steps are shown in Table I.
TABLE I. Processing Steps for Du Pont Type 275 Color Film.
1. Develop . . 2. Wash .... 3. First fix . .
.... 10-12 min .... 1-2 min .... 6 min
6. Wash 7. Second fix . . . . 8. Wash
. . 4 min . . 4 min . . 10 min
4. Wash .... 5. Bleach* . . .
.... 5 min .... 5 min
9. Dry
Note: If sulfiding of track is employed, this may be done after a 1-min wash following Step No. 5. Processing then proceeds to Step No. 6.