Calotype

The calotype emerged from a fundamental limitation of the daguerreotype: each daguerreotype was unique, a single unrepeatable image on a silver plate. What photography needed was a negative—an image that could produce unlimited positive copies. William Henry Fox Talbot's paper negative process would provide exactly that, establishing the negative-positive principle that dominated photography for 150 years.

Talbot had been working on 'photogenic drawing' since 1834, using silver chloride-sensitized paper to capture images. His early results were faint and required long exposures. When Daguerre announced his process in January 1839, Talbot rushed to publish his own work, but the daguerreotype's superior detail and clarity made it commercially dominant.

The breakthrough came in September 1840 when Talbot discovered 'latent image development.' He found that brief exposure created an invisible image in silver iodide paper, which could then be chemically developed to full visibility using gallic acid. This reduced exposure times from hours to minutes. He patented the process in February 1841, naming it 'calotype' from the Greek kalos (beautiful).

The calotype's key innovation was the paper negative. Light passing through the paper reversed tones: the negative showed dark where the original was light. By contact-printing this negative onto another sensitized paper, Talbot produced positive images with correct tones—and could make as many copies as desired from a single negative. This was photography's future.

Yet Talbot's aggressive patent enforcement in Britain limited the calotype's adoption. While the daguerreotype flourished in France and America (where Daguerre's process was freely available), British photographers faced licensing fees and legal threats. The calotype's commercial potential remained largely unrealized.

The negative-positive principle Talbot established became the foundation for collodion wet-plate photography (1851), gelatin dry plates (1871), and eventually roll film. Every photograph printed from a negative until digital imaging followed Talbot's insight: capture light once, reproduce the image infinitely.