Kalotype

Kalotype, also spelled calotype (and occasionally kalotype or Talbotype), is an early photographic process developed by Henry Fox Talbot in Britain during the 1840s. It introduced the negative–positive method that made multiple prints possible from a single image, a foundational concept for modern photography. The process used paper coated with a light-sensitive silver salt, typically silver iodide, which was exposed in a camera and then developed to form a negative image. Positive prints were produced by placing sensitized paper against the negative and exposing them to light, creating a reproducible photograph.

Process details. The sensitized paper was prepared by treating it with a solution that formed silver iodide on the surface. After exposure, a developer such as a gallic-acid solution reduced the latent image to metallic silver, yielding a negative. The negative was fixed and washed to remove unreacted salts. Prints were created by contact printing the negative onto another sheet of sensitized paper, and a final toning or washing step could affect the image’s tonal range.

Significance and reception. The kalotype was the first practical method to produce a reusable negative, enabling multiple copies of a scene and laying the groundwork for future photographic printing processes. However, calotypes were generally softer and less sharp than daguerreotypes, with longer exposure times, which limited their popularity for portrait work. Despite these limitations, the kalotype played a crucial role in establishing the negative–positive paradigm and influenced subsequent developments in photographic science and practice.