Owing to the complexity of the interactions among the components of a ceramic mixture, the same state of sintering can be achieved in different compositional systems at quite different temperatures. Thus the relationship between firing temperature and mineralogical composition of ancient ceramics is particularly interesting. Color determination, low magnification microscopy, and scratch or fracture tests are diagnostic tools to group the material. Phase analysis is accomplished with x-ray diffraction and/or thin-section microscopy. Scanning electron microscopy investigation provides evidence on textures and elemental compositions. If well-provenanced reference clays are available, scanning electron microscopy, ultrasonic attenuation, or thermal expansion measurements may be used in the comparison of textures. Electron-, nuclear-, or x-ray spectroscopy are also useful in the investigation of sherds. See also AATA 20-771.