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Photographers created their own glass plates and coated them with a solution of collodion (cellulose nitrate) and a soluble iodide.

The wet-collodion process is one of the earliest photographic processes.

The photograph, reportedly showing Lincoln at Gettysburg, is found within our Mathew Brady Civil War collection. The above image is a scan created from a copy negative made directly from the original wet-collodion glass plate negative. 111-B-4975 Crowd of citizens, soldiers, and etc. Let’s first look at two of the more popular 19 th century photographic processes, wet-collodion glass plate negatives and albumen prints, which are widely represented in our Civil War holdings. Wet-Collodion Glass Plates and Albumen Prints We do have a small number of daguerreotypes (direct positive process on silver plated copper), tintypes (direct positive process on a thin sheet of lacquered iron), and ambrotypes (underexposed glass plate placed against a dark background), but they are not as frequent as the other processes. For this post, I’ll be concentrating on the most prevalent processes and formats in our holdings. Photographic prints can be found in different print formats such as stereographs, cartes-de-visite and cabinet cards. Most prominent of these are our 19 th and early 20 th century holdings where you will find almost every early photographic process, including daguerreotypes, tintypes, ambrotypes, wet-collodion glass plates, gelatin dry plates, albumen prints, gelatin silver printing out prints, collodion silver printing out prints, matte collodion prints, platinum/palladium prints and cyanotypes.

In the Still Picture Branch, we have a wide range of photographic formats and processes that provide unique preservation challenges, including proper storage, proper handling and reproduction strategies. Not only do staff strive to become experts on the subject matter covered within our holdings, but also the physical format and the processes that made them. Working within the Special Media Division presents many challenges.