Eyeing the past: synchrotron µ-XANES and XRF imaging of tarnish distribution on 19th century daguerreotypes

Louis-Jacques-Mandé Daguerre introduced the first successful photographic process, the daguerreotype, in 1839. Tarnished regions on daguerreotypes supplied by the National Gallery of Canada were examined using scanning electron microscopy energy-dispersive X-ray spectroscopy and synchrotron-radiation analysis. Synchrotron X-ray fluorescence imaging visualized the distribution of sulfur and chlorine, two primary tarnish contributors, and showed that they were associated with the distribution of image particles on the surface. X-ray absorption near-edge structure spectroscopy determined the tarnish to be primarily composed of AgCl and Ag₂S. Au₂S, Au₂SO₄, HAuCl₄ and HgSO₄ were also observed to be minor contributors. Environmental contamination may be a source of these degradation compounds. Implications of these findings will be discussed.