Nondestructive Characterization and Enzyme Cleaning of Painted Surfaces: Assessment from the Macro to Nano Level

This work establishes a multiscale and multitechnique nondestructive approach as valid methodology for monitoring surface properties and evaluating the effectiveness of enzymatic removal of varnishes from paintings/polychrome artefacts.Mock-up samples (documented reconstructions of oil, tempera, and gilded layers on canvas and wooden supports) were covered with different proteinaceous varnishes (egg white, animal and fish glue, casein) and then characterized before and after the removal of these coatings with enzyme-based solutions. The varnish was cleaned in several steps (two dry swabs and two wet swabs) with a clearance step for removing the residues from proteinaceous varnish or from enzyme solution.Microscopy [stereomicroscopy (SM), optical microscopy (OM), atomic force microscopy (AFM), and scanning electron microscopy (SEM)] and colorimetric (CIE L*a*b* system) techniques were used for characterization of the reconstruction surfaces at different scales (macro-scale by SM and OM; micro-scale by SEM and nano-scale by AFM). These techniques were also used to monitor the cleaning treatment.Although results presented in this work were obtained for the specific treatment of enzyme removal, the methodology could be extended to other types of materials and cleaning. Further experiments on real works of art are needed for a complete validation of the methodology.

Starspots on by Dra-Type Stars

The first detection of spots on dwarf M stars was by Kron on YY Geminorum in 1948. Since then phenomena attributable to starspots have been found by numerous authors beginning with Kraft and Krzeminski on the star now known as BY Draconis and on CC Eridani by Evans. There is a close correlation between spottedness, Balmer emission and flaring in dwarf M stars. Evans appears to have been the first to attempt to analyse the small range light variations on spotted stars in terms of modulation caused by axial rotation. In comparison with the solar case one must assume that the spots are very large and long lived. There is also an ambiguity in dealing with very large dark spots as between a star with a dark area or a cool star with a bright area (the zebra effect— is a zebra a black animal with white stripes or a white animal with black stripes?). It is difficult to arrive at a solution for the spot parameters which is unique. In particular several analyses which have appeared have assumed that maximum light corresponds to the immaculate star whereas in fact the maximum light in the variation corresponds to the immaculate star dimmed by the light of any constant star abstraction.