Invented in the 1850s, the collodion process was the main method for making photographs for about 30 years, until the gelatin dry plate was invented in the 1880s. In recent years, wet-plate collodion has made a bit of a come-back. Of course, perhaps the most famous modern exponent of wet-plate collodion is Sally Mann. But many other modern photographers have used it, among them our own member, Peter Hrebien.
I recently came across wet-plate collodion portraits by Mark Luscombe-Whyte: