Ten samples of white and gray materials suspected of being plasters and four samples of carved gypsum bowls from neolithic and chalcolithic levels at Ali Kosh and Chagha Sefid were examined using an optical microscope and scanning electron microscope with simultaneous energy dispersive x-ray analysis in order to characterize the macrostructure, microstructure and elemental composition. The stone bowls were used as standards with which to compare the microstructure of the plasters.