Daguerreotypes and calotypes

After Niépce's death in 1833, his partner Louis Daguerre continued to experiment and by 1837 had created the first practical photographic process, which he named the daguerreotype and publicly unveiled in 1839.^[9] Daguerre treated a silver-plated sheet of copper with iodine vaporto give it a coating of light-sensitive silver iodide. After exposure in the camera, the image was developed by mercury vapor and fixed with a strong solution of ordinary salt (sodium chloride). Henry Fox Talbot perfected a different process, the calotype, in 1840. Both used cameras that were little different from Zahn's model, with a sensitized plate or sheet of paper placed in front of the viewing screen to record the image. Focusing was generally via sliding boxes.