Photochrom prints, also called Aäc, are ink-based images produced though “the direct photographic transfer of an original negative onto litho and chromographic printing plates.” – Library of Congress

Autochrome is an additive color ’screen-plate’ process: the medium contains a glass plate, overlaying random mosaic of microscopic grains of potato starch, with lampblack filling the space between grains, and an impermeable black-and-white, panchromatic silver halide emulsion. – Wikipedia

The system used two glass plates, one of which was the colour screen plate while the other was a standard black-and-white negative plate. The colour screen plate comprised a series of red, green and blue filters, laid down in a regular pattern of lines to form a réseau, or matrix. – Wikipedia