An approach to the dynamics of clay firing

Results of a detailed study on microtextural and microchemical characteristics of pottery obtained during different experimental firing runs carried out at different temperature under oxidising conditions are reported. During firing, the reaction behaviour of temper grains and clay matrix is dominated by disequilibrium conditions and characterised by the presence of different reacting sub-systems. Each one of them is compositionally well established and corresponds to different mineral phases in mutual contact. Reactions occur following the two main mechanisms: (i) reactions leading to nucleation and growth of new mineral phases (modal reactions) and (ii) reactions producing only compositional variations of phases (cryptic reactions). Modal reactions are given by new phases rimming the temper grains, whereas the cryptic reactions may develop during the partial transformation of a single phase, producing compositional zonings. Kinetic aspects are also considered in order to asses the role exerted by temperature, by bulk and mineral compositions and by fluid phase on the attainment of modal or cryptic reactions during firing.