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88 BRITISH KflSEMATOGRAPHY Vol. 16, No. 3
However, when live-action is involved, the negatives can be obtained in only one of two ways : either by using a three-strip camera, or from a multi-layer colour original.
Du Pont Color Positive
Du Pont Type 275 Color Release Positive has an unorthodox monopack structure, and also differs from all other commercial photographic materials in that a synthetic polymer replaces gelatine as a vehicle for the silver-halide. In fact, three different polymers are used, each one capable of forming an appropriate dye upon colour development ; in other words, the polymer molecules have colour forming structures attached to them.
It is interesting to learn from one of the several patents dealing with the new form of emulsion, that the silver-halide which forms the light-sensitive element of the layers is still precipitated in the presence of gelatine, and only after the basic emulsion has been made by normal procedure is the gelatine removed by centrifuging, and the silver-halides dispersed in solutions of the required polymer. By following this procedure, it is possible to make use of the complex speed and gradation bodies which are peculiar to gelatine ; and essential if anything more than a low speed and contrast is required.
The following description of the emulsion is taken from a Du Pont patent : — 8
fc'A protein-free photographic emulsion consisting essentially of a dispersion of light
sensitive halide in a hydrophylic synthetic linear polycarbonamide, containing recurring
intralinear oxygen atoms, in the ratio of one oxygen atom to each 7 to 16 carbon atoms,
and recurring intralinear amide groups, which polycarbonamide is insoluble in water
at 20 °C, but soluble to the extent of at least 5 per cent, by weight, in water containing
40 per cent, by weight ethenol at 70 CC."
The layer arrangement in Du Pont Color Release Positive departs from
normal in that the magenta component image is formed in the outermost layer,
the cyan image in the central layer and the yellow one in the layer next to
the base. The lowermost layer is green sensitive, the central layer red sensitive,
while the outer layer is non-sensitised. There is a yellow filter layer between
the blue and red sensitive emulsions.
R SENSITIVITY
(
DEVELOPED COLOR
BLUE
MAGENTA
Fig. 2. Cross
RED
S
CYAN
Section of
GREEN
YELLOW
Du Pont Color
ba/se
Release Positive
Printing and Processing Du Pont Stock
Printing must be carried out on a register pin step printer and the three exposures must be made through appropriate colour filters. The filters recommended by Du Pont are : —
Corning 5113 (Red) Corning 2403 (Blue) and Defender 60G (Green) These are relatively sharp-cut filters, but with an efficient optical system, using a 500-watt projection type lamp, it is possible to print each record at speeds of about 20-ft. per minute.
Processing follows normal colour development procedure, and sound tracks in silver sulphide can be obtained by roller application of a sulphiding solution between the bleaching and fixing operations.
One of the principal advantages claimed for Du Pont Type 275 is improved definition resulting from the extremely thin sensitive layers, and the relegation