Recovery of Degraded-Beyond-Recognition 19th Century Daguerreotypes with Rapid High Dynamic Range Elemental X-ray Fluorescence Imaging of Mercury L Emission

Madalena S Kozachuk,Tsun-Kong Sham,Ian Coulthard,Ronald R Martin,Andrew J Nelson,John P Mcelhone

doi:10.1038/s41598-018-27714-5

Madalena S Kozachuk, Tsun-Kong Sham + Show 4 more

Open Access

https://doi.org/10.1038/s41598-018-27714-5

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Abstract

A daguerreotype image, the first commercialized photographic process, is composed of silver-mercury, and often silver-mercury-gold amalgam particles on the surface of a silver-coated copper plate. Specular and diffuse reflectance of light from these image particles produces the range of gray tones that typify these 19th century images. By mapping the mercury distribution with rapid-scanning, synchrotron-based micro-X-ray fluorescence (μ-XRF) imaging, full portraits, which to the naked eye are obscured entirely by extensive corrosion, can be retrieved in a non-invasive, non-contact, and non-destructive manner. This work furthers the chemical understanding regarding the production of these images and suggests that mercury is retained in the image particles despite surface degradation. Most importantly, μ-XRF imaging provides curators with an image recovery method for degraded daguerreotypes, even if the artifact’s condition is beyond traditional conservation treatments.

Highlights

A daguerreotype image, the first commercialized photographic process, is composed of silver-mercury, and often silver-mercury-gold amalgam particles on the surface of a silver-coated copper plate
This work furthers the chemical understanding regarding the production of these images and suggests that mercury is retained in the image particles despite surface degradation
Mercury was chosen as it plays an integral role in the production process and its distribution mirrors that of the image particles that make up the photograph. Through this rapid-scanning μ-X-ray Fluorescence (XRF) imaging capability, we demonstrate that mapping the Hg Lα fluorescence signal can retrieve entire lost images, despite severe degradation

Summary

Introduction

A daguerreotype image, the first commercialized photographic process, is composed of silver-mercury, and often silver-mercury-gold amalgam particles on the surface of a silver-coated copper plate. Years later by Fizeau that involved pouring a gold-chloride-sodium thiosulfate solution over the plate, which was heated from below This deposited gold on the image surface via an electroless deposition process[12,13,14,15,16]. The daguerreotype image is created through specular and diffuse reflection of light from the silver-mercury-gold image particles on the surface. These image particles are formed when the photosensitized plate, which is covered with a silver halide (AgX), is exposed to reflected light from the object (e.g., an individual for a portrait). The interaction of light with the surface catalyzes the formation of silver particles[17], on the plate surface in densities proportional to the intensity of light (eq 1)[18]

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