. High fire porcelain glazes. . ws plainlywithin what wide limits the more fusible glazes fall. Cone 10 Burn.—In Figs. 6 and 7 are shown the results of thecone 10 burn. At this heat treatment only a small part of thefield is bright and the craze area comparatively large. It will be noted that there is a belt surrounding the bright areain which the glazes are of semimat appearance, and surroundingthis are glazes of mat appearance. The latter have the charac-teristic mat texture due to high alumina, while for the high silicaglazes the term mat appearance is used only as a criterion of 8 Technolo
. High fire porcelain glazes. . ws plainlywithin what wide limits the more fusible glazes fall. Cone 10 Burn.—In Figs. 6 and 7 are shown the results of thecone 10 burn. At this heat treatment only a small part of thefield is bright and the craze area comparatively large. It will be noted that there is a belt surrounding the bright areain which the glazes are of semimat appearance, and surroundingthis are glazes of mat appearance. The latter have the charac-teristic mat texture due to high alumina, while for the high silicaglazes the term mat appearance is used only as a criterion of 8 Technologic Papers of the Bureau of Standards maturity. Outside of the mat area the glazes are dry and imma-ture. Fig, 6 shows that the obvious way to correct crazing in thistype of glaze is to increase the alumina content by addition ofclay. Cone 12 Burn.—At cone 12, Figs. 8 and 9, the area of goodbright glazes has increased and the crazing area receded as wouldbe expected. Glazes 2, 3, and 4 show signs of overburning, as FLUX Z 5. FLINT PORCELAIN GLAZES CON£ 10 CLAY Fig. 7.—Porcelain glazes at cone 10 evidenced by the formation of bubbles which were not presentat cone 10. The semimat and mat areas have shifted position inaccordance with the change in the area of bright glazes. Glazes Cj, C2, C3, C,4 B3, B4, and B5, which are the high silicaglazes of lowest alumina content and the only glazes of 55 percent or more flint, show signs of segregation at this fire. Thisevidenced itself by lines on the surface of the glaze similar towatermarks, but rising from the surface instead of being depres-;sions. It appeared as if the fluxes were drawn to the inside ofthe glaze, leaving a skeleton of flint at the surface. With the con-traction of the body in burning, these high flint glazes did notfollow, and consequently had to rise from the surface of the body. High Fire Porcelain Glazes g Cone 14 Burn.—Figs. 10 and 11 show that at cone 14 the areaof bright glazes and the area of overburne
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