Mature Firing of Zisha Clay

A goal of all kiln designs and firing methodologies is to yield a mature (or “completely fired”) ceramic material. The desired level of vitrification varies between ceramic-material and, to a smaller extent, with the preferences of the materials users or patrons. A successful complete firing is predominantly determined by the firing schedule.

Completely fired zisha clay is vitreous[1], such that the feldspar has melted and the mullite crystals have formed; yet not vitrified, such that the surface is smooth and glassy[2]. During firing, early melting particles bring other compounds into the melt-solution; glass formed from melting feldspar and silicates in the clay body both melt and bond to mullite crystals within the pore structure[3]. The strength of fired zisha ceramics is a function of its firing schedule and the resulting formation of fused aggregate particles from partial vitrification: increased heat energy leads to greater shrinkage[4], higher densification, and lower porosity, resulting in a stronger-and-denser ware[5]. The solidification of the melt forms strong interlocking microstructure within the clay matrix.