These photographs are ambrotype portraits are of Confederate soldiers. The following is how the Library of Congress described what an ambrotype is and the process in which it was created:
The invention of wet collodion photography processes in the 1850s allowed the development of two new kinds of photographs–ambrotypes and tintypes. These new formats shared many characteristics with the earlier daguerreotypes but were quicker and cheaper to produce. Primarily used for portraiture . . . .
James Ambrose Cutting patented the ambrotype process in 1854. Ambrotypes were most popular in the mid-1850s to mid-1860s. Cartes de visite and other paper print photographs, easily available in multiple copies, replaced them.
An ambrotype is comprised of an underexposed glass negative placed against a dark background. The dark backing material creates a positive image. Photographers often applied pigments to the surface of the plate to add color, often tinting cheeks and lips red and adding gold highlights to jewelry, buttons, and belt buckles. Ambrotypes were sold in either cases or ornate frames to provide an attractive product and also to protect the negative with a cover glass and brass mat.