The first two workable processes from the late 1830’s were the Daguerreotype and the Calotype. Responsible for these were Niepce, Daguerre and Fox Talbot. The former two collaborated to produce the daguerreotype and the latter was the inventor of the Calotype. The daguerreotype is a positive image formed on a highly polished silver plate which was sensitized with iodine vapour and developed over mercury vapour!!!

The daguerreotype was capable of exquisite detail but suffered a couple of major drawbacks – namely, reflection and the fact that each image was unique, needing to be copied if extra images were required.

Calotypes on the other hand were made with a true negative/positive process able to produce multiple prints from the waxed paper negative. These didn’t have the extreme detail like the daguerreotype but the paper grain gave the prints a certain quality of their own.

In 1854 Frederick Scott Archer introduced the wet plate process which used a substance called collodion to hold various salts in suspension on a clear glass plate.

This produced very clear, sharp images in either negative or positive form. The negatives produced on the glass support could be printed onto paper or if slightly underexposed, developed in an oxidizing developer and placed against a black background, they appeared as positive images.

The positive image was named Ambrotype by the Americans and Collodion Positive on Glass by the British.

The advantages of the wet plate image were relatively shorter exposures and no troublesome glare as was common with daguerreotypes. Glass negatives produced by the process, although fragile had very long tonal range and superb detail unlike the Calotype.