Collotype Sharpness

Collotype became the most commonly used printing process for European postcards. This one is an example of a simple, single-impression card, printed in a blackish-green ink. Everett V. Meeks, whose name is stamped on the card, collected postcards and was the dean of Yale’s School of Art for thirty-five years.

The printing plate for collotype was prepared by coating a sheet of tempered ground glass with a layer of gelatin containing a bichromate, as a light-sensitizer, along with other ingredients—every collotype shop had its own secret formula. This coating was applied hot, as a liquid. Once poured onto the plate, it was dried by leveling the glass, protecting it from drafts, and applying a gentle heat. Next the plate was exposed with sunlight to a continuous-tone negative (as opposed to the halftone-bearing negative used in letterpress printing), then washed in cold water to remove the bichromate and swell the gelatin.

Collotype. Unknown Photographer. First Presbyterian Church erected 1756, Newburyport, Massachusetts. c. 1908. (Printed by The Rotograph Co., New York). 4 15/16 x 3 7/16" (12.6 x 8.7 cm). The Museum of Modern Art, New York. Gift of Richard Benson. A double-rolled collotype postcard in which the second inking was pale blue.

This wash was critical because it produced a reticulated pattern in the gelatin, providing a fine grain that allowed tiny spots of black ink to appear to the eye as varying tones of gray. Where the plate had been heavily exposed the reticulated gelatin would not take up water, and so would accept ink; the less-exposed areas would absorb water, reject the ink, and consequently print lighter. Once processed, the plate could be dried and stored for some time before printing. When it was to be used, the glass plate holding the gelatin image was soaked in water and glycerin, drained, and placed on the bed of the press.