Carbro print. William Rittase. Model with Umbrella. c. 1935. 13 1/2 x 10 3/8" (34.3 x 26.4 cm). The Museum of Modern Art, New York. Gift of Richard Benson. Carbro is a more flexible descendent of color carbon printing; it uses enlarged separations. Both carbro and color carbon require careful registration of the three color layers.

The making of color separations was the foundation of all color photography until the invention of single-sheet color materials, such as Kodachrome and Agfacolor, shortly before World War II. Those materials would use separations too, but they would be invisible, embedded in the multiple coatings of a new generation of color films and papers. In the meantime photo labs used separation negatives to make color carbons, color “carbros” (of which this picture is an example), and dye transfer prints. The carbro print was an odd duck. It was really a variation on the color carbon process, but it gained popularity in photo labs making color masters for the advertising trade. Color was moving onto the printing presses during World War II and separations would also be the basis for printing color in ink. There was a need for superb originals to be reproduced by the presses.
Since the ink separations then used would badly degrade the quality of the color, these originals had to be as good as possible. The carbro answered this need. It was controllable under lab conditions, used separations that could be manipulated and retouched, and became the color standard until the invention of modern color materials. The difference between the carbon and the carbro was in the separations and in the way the pigmented gelatin layers were hardened. Color carbon used full-sized separation negatives while the carbro used an intermediate set that were exposed to photographic paper to create a set of positives. These paper positives were bleached and placed in contact with pigment-bearing carbon tissue; the bleach migrated across to the gelatin and hardened it. After hardening, the tissue was transferred to the final support in exactly the same manner as in carbon printing.