On the Translucency of the Bodies consisting of Feldspar and Quartz

Four series of bodies were fired with the schedules shown in Fig. 1. Soaking was done only on the rapid (180°C/hr) fired bodies. Translucency of the fired bodies were measured by means of photo cell, and the relationships between the translucency and the microstructure of which the details have been reported in the previous papers were discussed with the following results:(1) Translucency of the bodies increased abruptly within a very narrow range of firing temperatures, and also increased greatly within a short period of soaking.(2) The temperatures at which translucency of the bodies abruptly increased, lie, e.g., in the case of firing rate of 60°C per hr., at about 1225°C for potash feldspar, and at 1210°C for soda feldspar, and these strictly coincide respectively with the temperatures at which dissolving of the feldspars progress suddenly.(3) Translucency of the bodies containing soda feldspar increased abruptly at lower temperatures than in the case of the bodies containing potash feldspar while, above these temperatures, translucency of the latter become markedly greater than that of the former. Causes of these inferiority of translucency of the bodies containing soda feldspar are inferred as follows:a) Soda feldspar usually comprises a solid solution of plagiociase having so large composition range, that its melting is continued up to the comparatively high temperatures.b) Viscosity of the soda feldspathic melt is lower than that of potash feldspathic one.c) Owing to these two reasons mentioned above, homogeneity of glasses formed in soda feldspathic bodies is largely inferior to that of potash feldspathic ones.d) Bubbles contained in soda feldspathic glasses are smaller and more abundant than in the case of potash feldspathic ones.(4) Addition of coarse grained quartz into feldspathic body, even if a few per cent, will result in a marked decrease of the translucency of the body, if the body will not be soaked at all. With increasing content of fine grained quartz, translucency of the body will also decrease, though not remarkable.(5) So far as the translucency of the body of the present system is concerned, soaking time is one of the most important factors.(6) It is confirmed again that the unhomogenity of optical density of glasses formed in the body is one of the most important factors affecting the translucency of the body, as has been reported in the previous gaper.