Recovering Past Reflections: X-Ray Fluorescence Imaging of Electrocleaned 19th Century Daguerreotypes

Abstract

The first commercially viable photographic image, the daguerreotype, captured imagesfor a span of approximately 20 years (1839–1860). Deterioration now disfigures many of thesevaluable images. One proposed restoration method is an electrochemical process. However, itssafety and effectiveness are still under debate within the conservation community as the effects ofthis treatment, and its physical and chemical impact on the daguerreotype image, have not yet beenanalyzed in depth. This study used synchrotron-based micro-X-ray fluorescence to map theelemental distribution pre- and post-electrocleaning on 19th century daguerreotypes using both softand hard incident X-rays. X-ray absorption spectroscopy was used to probe local chemistry beforeand after cleaning. Two different electro-treatment methods were compared: the original methodproposed by Barger and a second put forward by Wei. When used correctly, both processessignificantly reduced the S and Cl surface contamination without dulling the surface. However,both electrochemical methods used in this study resulted in a loss of Hg and Au from the surface.In all cases, the Hg distribution tracks with image particle density allowing the retrieval of fullportraits from entirely corroded daguerreotypes, suggesting that Hg concentration may be a usefulproxy for the original image.