I am testing a liner recipe supplied by Linda Christianson on two clay bodies, Earthstone Crank by Scarva and Rustic Stoneware by Potterycrafts, both iron-bearing bodies; the oxide content is similar in make-up. The recipe is intended for wood firing and hence, I suspect, a long cooling, but I fired several examples of each to 1280º in an electric kiln with two inspection holes open but did not open until cooled to 33º; in all, a 34+ hour firing. On the crank all pots crazed and some were still 'tinking' two or three hours after removal but on the rustic stoneware no crazing was apparent. Unfortunately the thermal expansion coefficients given by the suppliers are for different temperatures: the Crank being 4.5 x 10(-6) @1280ºC and the Rustic Stoneware 5.5 x 10(-6) @1260ºC. The Crank body appears to have a 20% lower exp.coeff. and should be the likeliest to cause the crazing. Is this correct? Any advice??
thanx pete