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Conservation often requires the removal of oxide layers from metal artifacts and new cleaning methods are being developed all the time. This paper provides a quantitative comparison of eight cleaning methods, three of which are mechanical (brushing or micro-blasting with Al2O3 or glass beads) and five of which are laser dependent (TEA CO2 or Nd:YAG laser, with or without surface water). Surface profilometry and scanning electron microscopy have been used to compare the cleaned surfaces with the original, known, surface geometries.

Results of laser cleaning experiments on different gilding types like leaf gilding and fire gilding are presented in this contribution by means of three tested art objects. The reflectivity of gold is advantageously high for the typical laser cleaning wavelength of 1,064 nm. Additionally, to avoid damage like gold loss, the transfer of the absorbed laser pulse energy into the art object by thermal conduction is considered. Fire gilded surfaces are most easily cleaned because of the good heat transfer conditions which imply a high threshold intensity with respect to damage. This is different for leaf gilded surfaces but suitable laser cleaning parameters have also been found for this case. The results of laser cleaning experiments are presented by photography, microscopy, SEM and EDX analysis.

This paper summarises the conservation of the Porta del Paradiso , currently underway. It briefly illustrates the two cleaning methods employed and the reasons leading to continue the cleaning of the perimeter panels with laser ablation, describing the various working phases.

In practical restoration – depending on the object in question and the regional attitude to monument restoration – widely differing techniques and restoration philosophies have been, and still are, applied to the exposure of metal. Depending on the type of metal, this results in differing working materials as well as highly diverging definitions of the required degree of exposure as far as removing corrosive deposits is concerned. Therefore, particularly where metallic or heat sensitive cultural assets are concerned, the applicability of an efficient cleaning procedure using contact-free laser beam technology, which is also gentle on the material, should be examined.

The Abergavenny Hoard is a recently discovered collection of late Saxon and Norman silver coins, the details of which were badly obscured by corrosion products and iron concretions. A Q-switched Nd:YAG laser, using near infrared radiation at 1,064 nm, was employed to clean the hoard. Detail retained on the surface of the coins after laser cleaning included “rough-out” marks and polishing marks from the original die, as well as the legend. From this evidence surface damage appears to have been minimal, and the treatment very successful.

The use of laser cleaning within the conservation field in the United Kingdom has tended to be restricted to indoor work within the studios of a small number of national museums and private conservation companies. This paper describes one of the first large-scale projects to be carried out on a public building in the United Kingdom.

The aim of this investigation and conservation study was to examine and evaluate the laser ablation method as a practical technique for cleaning of Indiana limestone, a calcite-cemented stone widely used in historic structures throughout the United States. To this goal, a thorough petrographic characterization of the samples was performed prior to and following laser cleaning tests by Q-switched and short free running Nd:YAG lasers. The main optimization problem was the amber-gray appearance associated with the laser ablation by Q-switching lasers. Following the evaluation of such a cleaning result, two practicable solutions based on suitable pulse duration or wavelength selections were successfully demonstrated and then compared with different intervention protocols proposed. This chapter will show that through this case study, an understanding of effective uses of cleaning highly weathered Indiana limestone through the use of three types of Q-switched and short free running Nd:YAG lasers can be most effective in the removal from limestone of surface soiling and thick built-up carbon deposits ranging from 0.5 to 1mm in thickness. Case study evaluation methods included petrographic examination of composition, texture, and microstructure using optical microscopy and scanning electron microscopy performed on thin and polished sections of limestone sampled from six areas before and after cleaning. The microscopy studies were supplemented with energy-dispersive X-ray spectroscopy to characterize crystalline phases and track changes in chemistry.

In Steyr, Austria, a Renaissance epitaph was cleaned by an Nd:YAG laser. Compared to cleaning tests, carried out with microsandblasting, (NH4)2CO3 and water compresses, the laser cleaning was much more sensible and faster. Satisfying results were realized for the calcareous sandstone of the frame as well as for the red and compact limestone of the relief. One of the big advantages was the detection of several traces of pigments, which were observed during the layered cleaning process. It can be assumed that other cleaning methods could not hold these last spots of polychrome surfaces. Care had to be taken of the energy. The application of higher energies on the red marble leads to colour changes into yellowish red.

Before starting the cleaning program of the peristyle of Diocletian Palace in Split, a series of tests have been performed on it. First of all, the state of conservation of columns and capitals has been assessed applying non-destructive techniques such as thermography, magnetoscopy and superficial ultrasonic tests. All the areas with black crusts, exfoliation and stone cracks have been determined. In this stage, parameters such as water absorption and colour have been estimated in order to compare them with those measured after the cleaning operation. Then, more than 3-month period of tests have been performed to set up all the parameters concerning the application of the laser cleaning techniques. In this chapter, the results of these preliminary investigations are presented.

This chapter deals with the cleaning of the Parthenon West Frieze by means of an innovative laser cleaning methodology. Following a comparative study of various cleaning methods, laser cleaning was proven to be the most efficient method for the removal of loose deposits and black crusts. The laser system employed is a Q-switched Nd:YAG system emitting at the fundamental and the third harmonic frequencies designed and developed by FORTH-IESL. The system emits in two wavelength beams individually or in combination. This feature, along with possible modification of the laser parameters – energy density, number of pulses, the contribution of each beam to the final combined beam – for each individual case of encrustation and substrate (marble, monochromatic layers), leads to a safe and controlled cleaning result. The project commenced in 2002 and was completed in January 2005. Since then, the Parthenon West Frieze is on display at the Acropolis Museum in Athens, Greece.