Surface characterisation of daguerreotypes with the optical metrological technique of confocal microscopy

Abstract

This paper presents non-perturbing techniques of optical and surface metrology applied to surface studies of daguerreotypes. Daguerreotypes are positive images developed directly on the surface of silvered copper plates. The image is a submicrometre, ultra fine structured surface that exceeds the resolving power of the optical microscope for surface examination. Confocal white light microscopy is shown to be a useful technique for examining the three-dimensional ultra fine structure of the daguerreotype image. This technique provides quantitative information of surface characteristics using established surface roughness parameters to document the daguerreotype surface. Examination at this level can measure changes due to environmentally induced deterioration and provide comparative data of before and after chemical and physical treatment. Confocal microscopy shows considerable potential in the evaluation and documentation of both daguerreotype condition and treatments performed on the image structure. Confocal microscopy was used in the close examination of the Southworth and Hawes portrait of an unidentified man and it demonstrated the ability to unambiguously identify and quantify surface damage. The daguerreotype of an unidentified woman wearing a bonnet was treated with ammonium hydroxide solution to remove tarnish and surface changes were followed with confocal microscopy.