The grey crusts covering some places of the weathered stained glass windows of Tours Cathedral were studied by Analytical Scanning Electron Microscopy. These crusts are constituted by a gypsum cement embedding many particles: microspherules (fly ash generated by combustion processes, rounded particles of leached glass, hypersiliceous spherules from tuffeau stone); angular fragments of leached glass; organic objects; siliceous and sulphated aggregates. The particles contained in the sulphated black crusts covering the stone, in the air and in the rain in Tours were studied simultaneously and compared with those of the stained glass windows grey crusts. In all cases, similar kinds of fly ash are present demonstrating the action of atmospheric microparticulate pollution both on the stained glass windows and on the stone.
