Negative-Positive Technic with the Dufaycolor Process

Progress in two directions has greatly simplified making prints from screen-film negatives. The study of emulsion characteristics and of the mechanics of development with silver bromide solvents has led to the avoidance of color dilution in copying one screen material from another. Sodium thiosulfate in a metol developer has been shown to localize development in the lower strata of the film, so that the silver image is formed in close contact with the reseau, largely eliminating scatter at the boundaries of differently colored units; the crystalline structure of the silver salts and grain-size frequency also assist in preventing scatter. Residual color dilution as the result of the 45-degree oriented reseaux is explained, and the way in which this has been counteracted by suitable choice of gammas in the negative and positive material. The production of a vapor-lamp emitting the line spectra of mercury and cadmium without appreciable spectral background, combined with a liquid didymium chloride filter has provided a triple monochromatic light-source, the spectral lines of which coincide with the peaks of the reseau transmissions, thereby eliminating dilution of color due to overlap, such as has always previously been present with color filters of the narrow-cut type. The Dufaycolor contact printing machine with automatic control of both hue and printing light is described. The technics of printing, and development with standard equipment, are described.

Print ISSN

0097-5834

Published

1938-09

Content type

Original Research

DOI

10.5594/J08480