Traditionally, the glazed surfaces of antique tiles have been cleaned by a mechanical process, or by using chemical solvents applied directly to the surface. These chemical and abrasive processes may result in accelerated degradation of the tile, particularly the fragile ceramic body, or in scratches on the glazed surface. Much useful conservation work has been accomplished using laser radiation, and this study describes an attempt to evaluate the usefulness of laser cleaning as a technique for ceramic tiles. ANd: YAG laser, outputting 1064 (infrared), 532 (visible, green) and 266nm (ultraviolet) radiation was used to clean dirty, glazed surfaces of eighteenth-century Portuguese tiles. To evaluate the results of the cleaning process, several analytical techniques, including optical microscopy, optical fibre spectroscopy and scanning electron microscopy, were used. Although the interaction with the surface was different at each wavelength, all the wavelengths tested were able to remove superficial dirt without damaging the underlying glazed surface, or the blue pigment; different ranges of jiuence were required for the successful use of the different wavelengths. Laser radiation with a wavelength of 532nm was found to be the most effective for cleaning. Radiation at 1064nm produced yellowing of the surface and incomplete dirt removal, while ultraviolet radiation (266nm) showed a very superficial action, resulting in a very slow material removal rate.
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