POLARIZED LIGHT MICROSCOPY IN CONSERVATION: A PERSONAL PERSPECTIVE
WALTER C. McCRONE
The advantages of microscopy are many. It is a direct method. EDS analysis tells us what elements are present but not what the compound is—for example, that calcium is present (could be whiting, gypsum, or anhydrite), or iron (could be Prussian blue or any iron earth pigment), or copper (could be malachite, azurite, copper resinate, verdigris, or blue verditer). The situation is little better if we find by FTIR a C-H stretching frequency and a carbonyl group.
Yet, again, I prefer to have and to use all three instruments. SEM/EDS quickly decides between vermilion and hematite, smalt and ultramarine; the FTIR/microscope is a quick and sure way to identify adhesives, varnishes, and media. With this arsenal of instruments—the polarized light microscope supplemented as necessary with SEM/EDS and the FTIR/microscope—there are few analytical problems of the conservator that cannot be solved.