Characterization of a Surface Tarnish Found on Daguerreotypes Revealed under Shortwave Ultraviolet Radiation

A characteristic fluorescent tarnish can be observed on some daguerreotypes under shortwave ultraviolet radiation. The fluorescence can be seen in several distinct patterns: edge tarnish, rings, and continuous films. Dispersive Raman spectroscopy, scanning electron microscopy (SEM), and X-ray diffraction (XRD) were applied to characterize and identify the fluorescent compound. Raman spectroscopy identified the characteristic peak for copper cyanide, CuCN, at 2172 cm- 1 . Elemental k-ratio maps of the SEM analysis indicated an increase in copper, sodium, carbon and nitrogen in the area of fluorescence. XRD confirmed the identification of a copper cyanide compound. Shortwave ultraviolet radiation can be used in a monitoring program of daguerreotypes to further characterize the fluorescent tarnish and its effect on the deterioration of daguerreotypes.