calotipo

Calotype, also known as talbotype, is an early photographic process developed by William Henry Fox Talbot and introduced in 1841. It is a negative–positive method that uses paper as the base material, enabling multiple positive prints from a single negative. The process marked a shift from single-image pictures to reproducible photographs.

The technique involves coating paper with a light-sensitive silver halide layer, typically silver iodide, and allowing it to dry. After exposure in a camera, a latent image is formed on the paper. The latent image is then developed chemically, usually with a developing solution containing gallic acid and silver nitrate, which reduces silver ions to metallic silver to produce a visible image. The paper is fixed with a hypo (sodium thiosulfate) solution to remove unexposed silver salts. The resulting negative can be used to produce positive prints by placing it in contact with another sheet of sensitized paper and exposing it to light, creating a calotype (talbotype) positive.

Calotypes were important because they introduced the true photographic negative, enabling repeated printing and broader distribution of images. However, negatives were relatively soft and lacked the fine detail of contemporaneous daguerreotypes, partly due to the texture of the paper substrate. The process required careful handling and longer exposure times.

The calotype laid groundwork for paper-based photographic printing and influenced subsequent methods, including salted and albumen prints, but the technique was eventually overtaken in the 1850s by the collodion wet plate process and other advances.