To produce a calotype, Talbot created a light-sensitive surface by coating a sheet of paper, usually writing paper, with a solution of silver nitrate. He dried the paper to some degree and coated it with potassium iodide to produce silver iodide. Prior to exposing the negative in the camera, Talbot gave the paper a final coating of a solution of silver nitrate mixed with acetic and gallic acids. The sensitized paper was then exposed in the camera.
The final step entailed fixing the calotype with hyposulfite of soda (hypo) or halides (potassium iodide and potassium bromide). Calotypes fixed with potassium iodide exhibited a yellow highlight tone. To produce a print with greater detail, Talbot often waxed the negative after processing. Wax penetrated the paper fibers making the negative more translucent. This process allowed more light to come through during printing and produced a print with less visible paper fibers.
While historically some have used the word “calotype” in reference to both early negative and positive images, the term “calotype” here refers to the paper negatives created with the process as developed by Talbot and used by the inventor, his circle of friends, and other amateur photographers of the time.