Ultrafast Laser Cleaning of Daguerreotypes
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Ultrafast Laser Cleaning of Daguerreotypes Michael J. Abere2, Ryan D. Murphy1,2,5, Bianca Jackson3, Gerard Mourou3, Michel Menu4, John Mansfield2 and Steven M. Yalisove2,5; 1
Applied Physics Program, University of Michigan, Ann Arbor, Michigan
2
Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan
3
Institut de Lumière Extrême, ENSTA, Paris, France
4
Centre de recherche et de restauration des musées du France, Paris, France.
Center for Solar and Thermal Energy Conversion, University of Michigan, Ann Arbor, Michigan 5
ABSTRACT An ultrafast laser irradiation method for the removal of corrosion from Daguerreotypes without detrimentally affecting image quality has been developed. Corrosion products such as silver oxide and silver sulfide may be removed by chemical cleaning but these reactions are hard to control and are often damaging to the underlying silver, ruining the image. The Ti:Sapphire 150 fs laser pulses used in this study are focused to a beam diameter of 60 ȝm and are normally incident to the Daguerreotype. It was found that the corrosion layer has a lower material removal threshold than silver allowing for removal of corrosion with minimal removal of vital information contained in the silver substrate. INTRODUCTION Daguerreotypes, the first means to capture photography, were created by Louis Daguerre in 1839. The process involved exposing a silver-coated copper plate to iodine with bromine or chlorine to form a light-sensitive plate. The plate was then placed in the focal plane of a camera and exposed to light in order to form a photograph. Silver/mercury amalgam microparticles form an ordered pattern on the surface that translates into an image for the viewer. The mercury is often replaced with gold during a gilding process to improve image stability. The particles range in size from 0.1-50 ȝm in diameter. Unfortunately, exposure to sulfur and moisture in the atmosphere over time causes an unattractive brown film to form over the image. The removal of this tarnish from daguerreotypes has been attempted many times before [1-4]. Chemical cleaning causes fading of the image due to damage to both the substrate and image particles. Low temperature plasma cleaning leaves faint white areas behind after cleaning and does irreversible damage to the silver substrate [1]. The most common means to restore daguerreotypes at present is electrocleaning, which refers to immersing the plate in an alkali solution with a silver electrode and running current through the system [4]. However, this process is ineffective in cleaning ungilded and colored plates. Cleaning daguerreotypes using an excimer laser (2.5 ns) was explored by Turovets et al. They observed removal of the tarnish without degradation to the image at
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fluencies of 0.1-0.12 J/cm [1]. The process was successful on both colored and ungilded plates. In cases where previous cleaning attempts had been made with cyanide, the threshold for melting the underlying silver was lower than that to remove the tarnish layer. Thus, remo
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