The deterioration of collodion wet-plate negatives made in the Mathew Brady Studios during the 1860s was investigated. The most seriously degraded plates were found to have saponified varnish coatings. Carboxylic acid metal salts in the varnish layer were determined by Fourier transform infrared spectroscopy. Subsequent identification of the metal ion as sodium by energy dispersive x- ray spectroscopy led to an investigation of the glass composition. Glass composition was measured by electron microprobe analysis, using wavelength-dispersive x-ray technique; the saponified varnish plates had glass substrates of the same composition, characterized by high sodium content.