There are two basic types of glass plate negatives - Collodion Wet Plate and Gelatine Dry Plate.

The Wet-Collodion Process: 1851
Collodion Wet Plate Negatives were in use from 1851 until the 1880s. They were invented by Frederick Scoff Archer, an English sculptor, who using a viscous solution of collodion, coated glass with light-sensitive silver salts. Because it was glass and not paper, wet glass plates created a sharper, more stable and detailed negative. Furthermore, a photographer could produce several prints from one negative. A Collodion wet plate negative can usually be identified by an unevenly coated emulsion, thick glass, rough edges, and sometimes a photographer's thumb print on the edge.

Dry Plates: 1871-1878
Silver Gelatine Dry Plate Negatives were invented by Dr. Richard L. Maddox and first became available in 1873. They were the first economically successful durable photographic medium. Unlike the wet plate variety gelatine dry plates were more easily transported, usable when dry, and needed less exposure to light than the wet plates. Other distinguishing features between the wet and dry variety were the thinner glass and a more evenly coated emulsion in the dry plate negative form. Dry plate glass negatives were in common use between the 1880s and the late 1920s.

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Glass Plates were replaced with the invention of flexible film by George Eastman in 1884