Evaluation of laser cleaning progress and quality

Conventional methods of surface cleaning in conservation of art works are based mainly on mechanical or chemical techniques which are individually selected by experienced conservator. Cleaning of delicate objects, diverse from the point of view of materials composition needs not only extended expert appraisements of used substances, but also minimization of possible damages, always present in the case of mechanical cleaning. These traditional methods are very diffi cult to control. Chemical reagent shows similar interaction in conservation of paintings, where chemicals penetrate technological painting layers and causes permanent, diffi cult in analysis cross-sectional alterations. Conservation practice shows necessity of frequent treatments of sophisticated objects with complex technological structure and individual preservation state, resulting from infl uence of diverse external factors as well as changes in original building material itself. Every detail requires individual, predetermined cleaning parameters, which causes that application of conventional conservation methods is limited and diffi cult. Laser technique gives possibility of almost full control of encrustation removal process at the surface of art works. Selective and precise interaction of light beam is fundamental advantage of non-invasive treatment of more or less tight unwanted surface layers. Specifi c properties of lasers, decreasing of systems costs, and reduction of dimensions of laser cleaning systems caused rising application of lasers in conservation [1-3]. Laser cleaning must be considered as an advanced tool applied in cases where traditional techniques may be inadequate. However, even if the last generation of laser systems has improved the comprehension of their effects and their engineering, laser cleaning is not yet a mature technology for earlier restoration tests, there is also lack of in-depth knowledge of the basic laser-artwork interaction mechanisms. There is still also a lack of diagnostic devices providing qualitative and quantitative information during the laser cleaning intervention. Application of laser radiation in physico-chemical surface analyses and structural objects investigations, have started simultaneously with development of laser cleaning systems. In the face of increasing interest in laser cleaning and diagnostic systems, important is acquaintance of the conservation community with the fundamental advantages and shortcomings of laser radiation in treatment and analysis of matter. In the present paper, authors describe and discuss selected areas of applications of lasers and optoelectronics in conservation of monuments and works of art, with particular attention paid to noninvasive, physico-chemical and structural analytical methods. Presented data are based on almost twenty years experience in laser cleaning and diagnostics of dozens priceless objects in Poland and abroad [4-6].