Many applications of Moessbauer spectroscopy in the field of ancient ceramics are based on the conclusions reached by research carried out on raw and fired clays. Of primary importance among these conclusions is the result which correlates the Moessbauer spectra with the form of the iron oxide phases and their particle size. This in turn has been correlated successfully with the firing temperature and the calcium content of the clay. Theoretically the firing temperature of an ancient ware can be derived by direct comparison of its magnetic ratio and ferric quadrupole splitting with the calibration curves of the fired clays. Refiring at high temperatures can also be useful for grouping of ancient wares and possible provenance determination. See also AATA 20-771.