Elemental Mapping of Historical Daguerreotypes Using Monochromatic Micro-XRF: Imaging, Degradation, and Conservation Potential

Abstract

The daguerreotype, introduced by Louis-Jacques-Mandé Daguerre in 1839, marked the beginning of photography. This early photographic process, based on halide-sensitized silver-coated copper plates developed with mercury vapor, produces highly reflective, image-bearing surfaces that are both visually unique and chemically complex. As part of the interdisciplinary Heritage Science project PHELETYPIA, this study investigates the surface morphology and elemental composition of two historical daguerreotypes from the Varaždin City Museum (Croatia) using monochromatic micro-x-ray fluorescence (μXRF), scanning electron microscopy with energy-dispersive x-ray spectrometry (SEM/EDS), and optical microscopy. By comparing elemental distribution maps based on Hg-L and Au-L lines, we assess the relationship between image particle composition, visual contrast, and degradation patterns. Our results suggest that differences in image formation and preservation are linked to original manufacturing processes, including uneven thermal development and subsequent environmental exposure. High-resolution elemental imaging reveals how visual information is distributed across tonal zones and how it may be affected by previous conservation interventions. These findings highlight the potential of non-invasive analytical imaging to enhance our understanding of daguerreotype image structure, support condition assessment, and inform long-term digital preservation strategies.