The Collotype is a photomechanical / lithographic-like process invented by Alphonse Louis Poitevin (1855) in which a pane of ground glass is coated with a bichromated gelatin. The coated glass is then baked to create a fine reticulated (grainy-mezzotint like) surface. The baked glass is next exposed to a negative under UV light and the bichromated gelatin hardens in proportion to the exposure, as in a gum bichromate print. The plate is then washed, so that the unexposed / unhardened gelatin washes out, and then coated with glycerin. The glycerin coating allows the remaining bichromate to be hygroscopic (able to absorb moisture from the air) in proportion to the degree of the bichromate’s exposure. To make a print, the plate is rolled with greasy lithographer’s ink; the ink adheres to the exposed areas of the plate with the least water content, and then printed on paper. Commercial usage was common following the perfection of the process by Joseph Albert in 1868.

The Calotype, invented by William Henry Fox Talbot in 1835, is the name for the first photographic process to produce a negative that would facilitate the making of a direct positive. In the Calotype process a piece of high-quality writing paper is sensitized with a solution of silver iodide: potassium iodide and silver nitrate. Prior to exposure, a second solution of silver nitrate, acetic acid, and Gallic acid is applied to the paper (increasing the light sensitivity), dried, and exposed to UV light. The exposed image is then re-sensitized with a solution of gallo nitrate of silver (Gallic acid and silver nitrate) that causes the latent image to emerge. The print is then fixed in a solution of potassium bromide or sodium chloride, and after it has dried, used as a negative (sometimes waxed, or oiled, to enhance the transparency of the paper negative) in contact with a newly sensitized piece of paper to produce a direct positive. This process, following some improvements, was renamed the Talbotype and is, in current definition, much like a salted paper print. In 1844, Talbot published the second photographically illustrated book, The Pencil of Nature, hand tipping his Calotypes throughout the manuscript.