Ceramics-Silikáty 47 (3) 100-107 (2003)

INFLUENCE OF THE THERMAL EXPANSION MISMATCH BETWEEN BODY AND GLAZE ON THE CRACK DENSITY OF GLAZED CERAMICS

B. Plešingerová, M. Kovalčíková

The genuine craquellé decor is created by a sufficient tensile stress in the glaze, which causes the glaze cracking during the cooling and creates the required crack-net. When slow cooling of the glazed ware is secured the characteristic crack-net is formed if the difference of the linear thermal expansion coefficient (DTEC) of the body and the glaze is in the range of (-36 to -65) x 10^-7 K^-1. The cracks are so deep that they reach the body. The porous ceramic body that is characterised by the moisture expansion is not very suitable for the craquellé. In that case, the formation of cracks continues after cooling and additional thin cracks appear in the glaze. The results of tests of the crazing glazes showed that the intensity and design of cracks depend on the composition and combination of the glazes, too. Nice and interesting craquellés have been created in the prepared crazing glazes if DTEC (body-crazing glaze) was in the range of (-33 to -46) x 10^-7 K^-1.

Keywords: Glaze thermal expansion coefficient, Cracks, Art decor - craquellé, Crazing glaze