This paper presents the results of investigations on temper, paste, and porosity of ancient ceramics by application of optical microscopy, x-ray diffractometry, and measurement of porosity. Porosity data must be interpreted carefully; the results of controlled firing and refiring of illitic calcareous and kaolinitic noncalcareous clays show how difficult their interpretation in terms of ancient firing temperatures and initial granulometry can be. The effect of reducing atmosphere is also discussed. Much more research work is needed, however, before porosity data can be interpreted correctly. The mineralogical changes during firing of the paste are very useful for an estimation of the ancient firing temperature, the nature of the raw material, the technology of the processing and firing atmosphere. Firing experiments on kaolinitic non calcareous and illitic calcareous clays are discussed. There is a great need for more detailed research, especially with respect to reducing firing conditions. A review of the mineralogical changes during burial leading to secondary products as calcite, montmorillonite, mixed-layers, and zeolites is presented. Finally, the application of temper analysis for identification of local or foreign production of coarse ware is discussed, and arguments for identifying artificially added temper are presented. See also AATA 20-771.