THE PRICE OF PRISTINE PMMA
BY YVONNE SHASHOUA, ANJA LISS PETERSEN, ESTHER RAPOPORT
Many publications by conservation professionals describe visual assessment as the primary evaluation technique for cleaning. This may be due to the lack of analytical equipment available in museums, the speed and simplicity of visual examination or to the great importance of appearance of museum objects. Although it is relatively simple to examine surfaces by eye, it is complex to convey the results to others and it is unlikely that two independent evaluators can achieve identical results. Optical microscopy provides qualitative results concerning the intensity and density of scratches induced when cleaning and the presence of residues left by cleaning agents. Gloss measurements are relatively easy to perform and provide information about the presence of any physical changes to surfaces. However, when examining transparent plastics, measurements are disturbed by the multiple reflections within the bulk of material. Contact angles are relatively easy to perform and show changes in surfaces often before they can be detected by eye or optical microscopy. Contact angles relate to the type of change including the introduction of residues or of scratches, although it is not simple to attribute causes. Contact angle measurements can offer a reproducible and quantitative alternative to visual appearance for conservation professionals.