Carbon transfer, often also called autotype from the name of a company which made carbon tissue, is one of the most important permanent techniques designed with the specific purpose of giving images permanence.
In this particular technique, the image, though invisible, is first formed in a layer of pigmented gelatin sensitized with dichromate. It is then transferred onto a sheet of specially prepared paper. Unlike the other chromium based processes, carbon transfer allows the photographer to create images of absolute sharpness and perfect contrast.