Characterization of pre-pottery Neolithic and Egyptian plasters has been carried out, with emphasis on microstructural observation with the scanning electron microscope. Samples from Asikli Hüyük, Çayönü Tepesi, Tell Ramad, and Jerico were examined; the results show that true lime plasters were utilized in the aceramic Neolithic. The quantity of material used and the temperature necessary for limestone calcination imply that some sort of crude kilns must have been emploted. The availability of this technology makes understandable the subsequent rapid development of fired pottery. Samples of Egyptian plaster from Timna (ca. 1400-1200 B.C.) were found to be lime, contradicting Lucas' statement that lime plasters were unknown in Egypt prior to the Ptolemaic period. Gypsum plasters of both Neolithic and Egyptian origin have also been characterized.