Daguerreotype
Invented by Louis-Jacques-Mandé Daguerre and introduced worldwide in 1839, daguerreotype was almost completely superseded by 1860 with new, less expensive processes yielding more readily viewable images. In the late 20th century, there was a revival of daguerreotypy by a small number of photographers interested in making artistic use of early photographic processes.
Henry Collen
Calotype was an early photographic process developed by Henry Fox Talbot who was a colleague of Collen's. Talbot supplied the photographic knowledge and Collen the artistic know-how. In an article titled "Photography in the 1840s," Peter Marshall describes the distinction between daguerreotypes and calotypes. "The daguerrotype spread rapidly around the world...There were some limitations on the spread." Daguerre's process was somewhat limited by his prior patent in the UK, and so only those professionals who could afford a license were able to do so. Meanwhile, Talbot patented his calotype process in the UK and the US, but he was unable to get a patent in France which also limited its growth. Also, Marshall states, "In general, most professional photographers used the daguerreotype process in the 1840s, while the calotype was generally favored by those who were not attempting to earn an income." (A chart describing the differences between calotypes and daguerreotypes is included in the Appendix).