The project of interlaboratory research included: 1) determination of the precise composition of 5 potsherds to serve as standards; 2) selection of the most appropriate techniques for these analyses. Nine French laboratories and two in the U.S.A. agreed to participate. 51 medieval ceramics from excavations in Normandy and Anjou were used for comparitive analysis of major, minor and trace elements. The results are shown in 11 tables. The authors describe the x-ray fluorescent spectrometry method used by French museums and quantitative x-ray diffraction to evaluate the percentage of sand.