Collotype is a gelatin-based photographic printing process invented by Alphonse Poitevin in 1855 to print images in a wide variety of tones without the need for halftone screens. The majority of collotypes were produced between the 1870s and 1920s. It was the first form of photolithography. Invention Collotype originates front the Greek word "kola" for glue. Poitevin patented the idea of collotype printing the same year it was invented in 1855. The process was shown in 1859 by F. Joubert. Process Poitevin's Collotype In Poitevin's process, a lithographic stone was coated with a light-sensitive gelatin solution and exposed to a photographic transparency. The gelatin would harden in exposed areas, leading to the stone becoming hydrophobic in light areas (and thus, ink-repelling) and hydrophilic under dark areas (ink-attracting). The stone was then printed via the standard lithographic process, producing a monochrome print. 1860s Developments In 1865, Tessie du Motay and C. R. Marechal applied the gelatin to a copper plate, which was easier to handle than a lithographic stone. However, the gelatin did not adhere well and limited print runs to about 100. In 1868, Joseph Albert and Jakub Husník applied a gelatin-albumen mixture to glass, which was then coated with light-sensitized gelatin. This allowed print runs of up to 1,000. This patent was later purchased by Edward Bierstadt, who developed one of the first commercial collotype companies in New York City. Later collotype The collotype plate is made by coating a plate of glass or metal with a substrate composed of gelatin or other colloid and hardening it. Then it is coated with a thick coat of dichromated gelatin and dried carefully at a controlled temperature (a little over 50° Celsius) so it "reticulates" or breaks up into a finely grained pattern when washed later in approximately 16 °C water. The plate is then exposed in contact with the negative using an ultraviolet (UV) source which changes the ability of the exposed gelatin to absorb water later. The plate is developed by carefully washing out the dichromate salt and dried without heat. The plate is left in a cool dry place to cure for 24 hours before using it to print. Related processes, or processes developed from collotype, or even alternate names for collotype include albertype, alethetype, autocopyist, artotype, gelatinotypy, heliotype, hydrotype, indotint, ink-photo, leimtype, lichtdruck, papryrotype, photogelatin, photophane, phototype, Roto-Collotype, Rye’s, and Sinop. Color collotype or chromocollotype In 1874,