Ancient 'gilded' art objects from European cultural heritage: a review on different scales of characterization

This paper is a review on the studies performed through imaging and spectroscopy-based analytical methods on ancient 'gilded' art-objects (9th-19th centuries) from the European cultural heritage. The review takes into consideration the gilded surfaces in polychrome art objects (easel and mural paintings, polychrome wooden objects, gilt leather and parchment), thus meaning the materials and techniques of application of gold or its imitations (silver, copper leaves, other metal alloys) from technical, analytical and conservation points of view. The characterization of artistic gilded objects is important for establishing the compositional, structural, morphological and physical-chemical parameters useful for monitoring the conservation state, behavior and evolution in time of their aging/degradation/deterioration processes, the restoration treatments (cleaning, consolidation, retouching, varnishing) influence on the conservation state of the original materials and also for a rationale choice of methods and materials of intervention, compatible with the original ones. The analytical approach has, as main requirement, to be noninvasive and non-or microdestructive, therefore, sampling is to be avoided or reduced to a minimum. A wide range of imaging and spectroscopy-based techniques is nowadays available from optical microscopy, UV fluorescence photography, IR reflectography, X-radiography, thermography, to scanning/transmission/environmental electron microscopy (SEM/TEM, E-SEM), atomic force microscopy (AFM), FTIR and Raman microscopy (micro-FTIR, micro-Raman), X-ray spectrometry (WDXRF/EDXRF/ TXRF, XPS), Ion Beam Analyses (PIXE/PIGE, RBS, SR), etc. The most reliable and complete information can be obtained from an integrated, complementary and interdisciplinary approach, but microscopy still remains one of the most used and efficient tools in the characterization of gilding materials and their application techniques. Copyright (C) 2011 John Wiley & Sons, Ltd.