The two materials (diaminodiphenylmethane and sulphur) were mixed together on a microscope slide and melted under a cover glass. As soon as melting of all the constituents was complete, the cover glass was pressed down in order to reduce the thickness of the preparation and the slide quickly removed from the hotplate (an inverted electric iron is a good substitute). The specimen was photographed under crossed polarized illumination. The objective was a plan apochromat 10x/0.32 NA coupled to an achromatic condenser. The microscope was a Zeiss Ultraphot III equipped with an automatic 35-millimeter photohead. The film was Fujichrome Velvia. (10x)