はち物容器に関する研究

Abstract

Experiments were carried out to estimate optimum firing temperatures of clay flowerpots with special reference to the permeability to air and water.Test pieces of about 4cm in dia. and 0.5cm thick were made from seven clay materials in different districts. These pieces were air dried for several days before oven-drying overnight at 50°C. Then, they were fired at different temperatures ranging from 250°C to 1, 050°C for one hour. The rising rate was 100°C per hour until respective temperature was obtained.1. Permeability to air of all samples increased at above 460°C of firing temperature. At above 875°C, these samples could be classified in three groups. At first, clay materials of Hekinan (E) and Takahama (F) cities in Mikawa district, and of Makabe (C) remarkably increased permeability to air up to 1, 045°C. However, permeability to air of Makabe′s clay (C) decreased extremely at 1, 125°C. Next, permeability of both materials of Tokyo (A and B), which are native in Yashio city, Saitama pref., decreased considerably at 1, 045°C. The third group including clay of Kitaibaraki (D) and Tokoname (G) had a little lower permeability than the others at every firing temperature and there were less remarkable changes up to 1, 045°C.2. Changes of the permeability to water in relation to the firing temperatures or kinds of clay were almost the same as those of the permeability to air. However, values of the permeability to water were generally about 1/300-1/500 of those of the permeability to air.3. Curves of the relation between the water absorption or the apparent porosity and firing temperatures were very much alike. Both of them did not change appreciably up to 875°C, but had a sudden decrease at 1, 045°C, especially for two samples of Tokyo (A and B).4. There was no remarkable difference in the apparent specific gravity among the samples to 875°C except Makabe (C), but the values of all samples decreased at 1, 045°C. While, the bulk specific gravity of all samples increased very much at 1, 045°C, especially for the two samples of Tokyo (A and B).5. The results obtained in these experiments suggest that non-refractory clay of Yashio city (A and B) should be fired at lower temperatures than the others, Mikawa (E and F) and Makabe (C) clay at relatively high temperatures, and the Kitaibaraki (D) at the highest. These results also suggest that the characteristics of clay materials are related essentially to the determination of the firing temperature of clay flowerpots, and that clay pots have been produced successfully at ample firing temperatures.