A Study of the Effect of the Wavelength in the Q-Switched Nd:Yag Laser Cleaning of Gilded Wood

Pedro Gaspar (a) , Manuela Rocha (b) , Aileen Kearns (c) , Ken Watkins (c) , Rui Vilar (d)

(a) Conservation Department, Victoria & Albert Museum, South Kensington, London SW7 2RL, UK
(b) Tacula-Marcenaria e Restauro, Lda., Rua do Se´ culo N16, 1200 Lisbon, Portugal
(c) Department of Mechanical Engineering, University of Liverpool, Liverpool L69 3GH, UK
(d) Department of Materials Engineering, Instituto Superior Te´ cnico, Av. Rovisco Pais, 1056 Lisbon, Portugal

The removal of a brass-based paint (purpurin) used in painting gilded wood to cover losses of gold leaf, represents today a difficult task to conservators, who may have to resort to toxic chemical solvents in order to clean the painted surface. This action, due to its nature, is unsuitable for both the conservator and the artwork itself. In this study, a Q-switched Nd:YAG laser system outputting 1 064 nm (infrared), 532 nm (visible, green) and 266 nm (ultra-violet) radiation was used to study the interaction of these wavelengths in a gilded sample surface painted with purpurin. All tested wavelengths interacted differently with the tested surface and, also, the several layers that form the gilded surface (purpurin, varnish and gold) showed different interactions to each wavelength. The ultra-violet radiation (266 nm), in a multi-pulse mode at low fluences, was found to be the most efficient wavelength in cleaning the painted gilded surface.
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