CORRELATION OF GLAZE-BODY STRESSES WITH THERMAL PROPERTIES OF WHITEWARE BODIES*

Several lead borosilicate glazes with high to low thermal expansion were applied to a bisque whiteware body having porosities ranging from 20 to 30%, and the thermal properties were studied. Test pieces were subjected to an autoclave test at 50, 150, and 300 lb. per sq. in. and to a thermal-shock test by quenching from 400° to 600°F. into cold water. The thermal-expansion curves for the various glazes and for the body at each porosity were determined on the interferometer. The glaze-fit ring test was used to determine the degree of tensile and compressive stress, and these stresses were plotted graphically with the body porosity. The resistance to crazing was increased in both the autoclave and thermal-shock tests as the thermal expansion of the glazes, as measured on the interferometer, decreased. The 10% porosity body gave the best results in the thermal-shock test. A close correlation was found between the thermal-expansion curves for the glazes and bodies of varying porosity and the stress characteristics shown by the glaze-fit ring test.