Abstract
We report on the elemental and chemical characterization of tarnish on a historic daguerreotype plate. Scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) spectroscopy reveal the presence of C, O, Na, K, P, Cl, Hg, Ag, Cu, S and Au. Synchrotron based X-ray absorption near edge structure (XANES) spectroscopy, together with two-dimensional X-ray fluorescence (XRF) microscopy, provide information beyond the elemental distribution and speciation of the daguerreian tarnish features, revealing the presence of NaCl, KCl, HgCl2, HgSO4, CuS, and Ag2S on the surface. Through the application of synchrotron XRF, the distributions of Ag and S were found to be inversely correlated. This suggests a preferential accumulation of S within high-density particle regions. Spectroscopic investigation at different regions within the XRF image showed that blemish regions contained degradation products such as NaCl and KCl with AgCl noted in the surrounding regions. The observation of Cu on the surface, in the form of CuS, may either be a result of Cu diffusing through grain boundaries and/or holes in the Ag, or from the accretion of Cu salts, such as basic sodium copper carbonate, from the deterioration of the above cover glass. Silver halides (AgCl, AgBr and AgI) were also detected with XANES. This may be the result of either environmental conditions or from residual products from the production process of the plate. These results point to the interaction between deterioration products from the cover glass with the daguerreotype surface as one, but not the only, source of the tarnish.
Highlights
Eighteen thirty-nine saw the invention of the first recognized, commercial form of the photograph, the daguerreotype, which was named after its inventor, Louis-Jacques-Mandé Daguerre
First optical microscopy and Scanning electron microscopy (SEM) were used to identify image particles associated with the tone and brightness of selected regions, as well as tarnish features
While some smaller particles were observed in the shadow region alongside the image agglomerates, which are not expected in the shadow region, they may be the result of the photo-catalyzed reaction to Ag particles from the invasive AgCl that covers the surface
Summary
Eighteen thirty-nine saw the invention of the first recognized, commercial form of the photograph, the daguerreotype, which was named after its inventor, Louis-Jacques-Mandé Daguerre. The daguerreotype process was used to document individuals and landscapes for approximately 30 years; these images are important objects of historic significance. The daguerreian image is the result of reflection and refraction of light off image particles that vary in shape and distribution. This yields the range of gray tones that typify. The conservation of these historic artifacts is a challenge for conservators and scientists. Daguerreotypes are prone to corrode under ambient conditions resulting in the production of metal oxides and sulfides that generate haze and spots across the surface [4, p.
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