Talbotype

Talbotype, also known as the calotype, is an early photographic process developed by William Henry Fox Talbot in the 1830s and publicly demonstrated in the 1840s. It is a negative-positive system in which a paper support is made light-sensitive so that negatives can be used to produce multiple positives. The method is one of the first practical approaches to reproducible photography.

The process begins with preparing paper by saturating it with light-sensitive silver salts. A common sequence involved treating paper with a solution of silver nitrate followed by potassium iodide to form silver iodide on the surface. After drying, the paper is exposed in a camera; the areas that receive more light form a latent image. The latent image is then developed, traditionally with a developing solution containing gallic acid (and often a trace of silver salts), which reduces the exposed silver compounds to metallic silver, creating a visible negative image on the paper. The negative is usually fixed and washed to remove unused salts.

Prints are made by contact printing a second sheet of sensitized paper against the negative, yielding a positive image. Calotype negatives were valued for their ability to produce numerous prints from a single negative, but they tended to be softer and less sharp than daguerreotypes, with visible paper texture contributing to a characteristic quality. The process required long exposure times and careful handling of chemicals, and it competed with other early methods such as the daguerreotype and the salted paper print.

The talbotype/calotype helped establish the concept of negative-positive photography and influenced later photographic development. It gradually declined with the advent of more sensitive and sharper processes in the mid-19th century, such as the wet collodion process.