Synchrotron Radiation Analysis of Daguerreotypes: Surface Characterization, Electrocleaning, and Preservation

Madalena S. Kozachuk, The University of Western Ontario

Abstract

The first commercially viable photographic image, the daguerreotype, captured images from 1839 to 1860. While daguerreotypes provide a significant historical record of 19^th century individuals and events, deterioration now disfigures many of these images. This work describes the application of synchrotron radiation (SR) to the study of daguerreotypes.

Three goals were addressed in this thesis: 1) to utilize SR to further elucidate the physics and chemistry of the daguerreotype and how the surface varies with time, 2) to study the effects of the electrocleaning system on the daguerreotype surface, and 3) to propose suggestions to improve their preservation and restoration efforts.

The collection of the Ag and Au L₃-edges from a daguerreotype test plate showed that the image particles on the surface form an alloy with a fcc structure and that the degree of Au diffusion into the Ag plate differed across the surface. This variation in diffusion produced an average alloy composition of Ag₉₀Au₁₀ (shadow and midtone regions) and Ag₇₃Au₂₇ (highlight region). Finally, both lab and SR sourced X-ray photoelectron spectroscopy showed Hg was present only within the first 1-2 nm of the surface and that alloying with Ag was possible but not consistent across all regions.

Expanding to 19^th century plates, the primary tarnish on the surface was Ag₂S and AgCl. X-ray fluorescence (XRF) found S and Cl to accumulate on high-density image particle regions. S K-edge suggested a possible Hg-S interaction, corroborating minimal amalgamation between Hg and Ag.

XRF of the eye region noted a variety of deterioration compounds and blemishes, which were removed when treated electrochemically by both the Barger (1982) and Wei (2011) methods. Full plate XRF imaging revealed that while the Hg L emission retained a great deal of information both before and after cleaning that Au and Hg were removed: the Barger method had the greatest impact on the relative concentrations of Au, while Hg appears to be removed in similar quantities by both the Wei and Barger process. Importantly, this work presents a method that allows, for the very first time, the retrieval of fine daguerreotype images tarnished beyond recognition.