Characterization of a Surface Tarnish Found on Daguerreotypes Revealed under Shortwave Ultraviolet Radiation
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Characterization of a Surface Tarnish Found on Daguerreotypes Revealed under Shortwave Ultraviolet Radiation Aaron Shugar1, Krista Lough1, Jiuan Jiuan Chen1. 1 Art Conservation Department, SUNY Buffalo State, Buffalo, New York, USA. ABSTRACT 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. INTRODUCTION Ultraviolet radiation is a common technique employed in conservation to examine a variety of art and artifacts including paintings, objects, paper, and photographs [1]. Shortwave ultraviolet radiation (UVC, 200 – 280 nm with the peak at 254 nm) was first used to examine daguerreotypes in 1992 [2]. It was observed that some daguerreotypes produced a bright green fluorescence examined under UVC. Early research on this phenomenon documented the occurrence of this fluorescence in daguerreotype collections, and made advancements in its initial identification. The extent at which this phenomenon was identified was extensive with 50% of the collection investigated showing fluorescence [2, 3]. Although initial attempts to characterize the cause of the fluorescence were made, they were by no means conclusive. Non-destructive and non-invasive analysis is essential when working with daguerreotypes. This is due to the sensitivity of the image surface. Even though direct sampling can potentially provide additional information, it is not recommended, nor would it be reproducible on daguerreotype plates not deemed sacrificial. Therefore, this research focuses on in-situ analysis to avoid removing the tarnish, limiting the damage to the plate itself, and suggests a non-invasive method of identification for other researchers. This research focuses on the characterization of the fluorescence through different analytical techniques, including dispersive Raman spectroscopy, scanning electron microscopy (SEM) using elemental k-ratio maps, and X-ray diffraction (XRD). Several mockups were produced and the daguerreotype selected for analysis exhibited strong fluorescence, possibly indicating a greater amount of the fluorescent compound.
Background Research The use of UVC for the investigation of daguerreotypes was first discussed by Daffner, Kushel, and Messinger [2]. Their research includes a description of a tarnish that occurs on some daguer
