Presentation Information
[O12-P30]Feasibility of using soil from the Sagano High School Woods for Field Studies as glaze: Successful soil for Sagano Yaki
*Sayaka Seno1 (1. Kyoto Prefectual Sagano High School)
Keywords:
Clay minerals,Sagano High School Woods for Field Studies,Porcelain clay
Introduction
We have been aiming to make “Sagano Yaki” by using residual soil derived from weathered rock in the Sagano High School Woods for Field Studies; hereafter, the soil derived from this site is referred to as SWFS soil.(Nakagawa, 2025). The clay of SWFS is considered difficult for potters to handle because it contains coarse sand fractions and has little silt fraction (Taniguchi et al, 2024). However, Ijiri (2024) analysed the grain size composition and reported that SWFS soil is viable as a ceramic clay, suggesting that its handling characteristics can be regarded as a distinctive property rather than a limitation.
One application of clay materials is in the preparation of ceramic glazes. Glazes created by potters are sometimes made from locally sourced materials such as clay and ash. Since the soil from SWFS can also be used as clay, it is considered that it may likewise be suitable for use in glazes.
The aim of this study is to evaluate the potential of SWFS soil as a ceramic glaze material.
Method
Glazes were prepared using SWFS soil, applied to bisque-fired test pieces, and then fired. The resulting ceramics were evaluated for their physical properties using the Mohs hardness test and a water absorption test, with a commercially available transparent glaze used as the comparison standard.
The test pieces were fabricated by shaping white clay into disk forms with a diameter of 5 cm and a thickness of 1 cm, followed by firing at 800 °C for 6 hours. The handmade glazes consisted of four types of samples made from SWFS soil sieved to particle sizes below 2 mm and 0.25 mm, with and without water elutriation. Commercially available ash was used as a fluxing agent. The mass ratios of soil to ash were set at 5:0, 4:1, 3:2, 2:3, and 1:4, yielding a total of 20 glaze compositions (4 sample types × 5 ratios). For each composition, 0.8 mL of water was added per 1.0 g of the combined soil and ash, and the mixture was applied to the test pieces. The coated samples were fired in a tabletop muffle furnace (Daiken Corporation) and a Rakuraku kiln (Good Electric Corporation), heated at a rate of 20 °C min to target temperatures of 1000, 1100, 1200, and 1250 °C, and held at the target temperature for 14 hours.
The fired products were evaluated using the Mohs hardness test and a water absorption test. The water absorption test was conducted in accordance with the JIS standard method for measuring the water absorption and specific gravity of refractory bricks (Watanabe, 2023). Water absorption (%) was calculated as: Water absorption (%) = [(mass in saturated state - mass in dry state) / mass in dry state] / specific gravity of immersion liquid × 100. Pure water was used as the immersion liquid.
Results and Discussion
When fired using only the SWFS soil or at a firing temperature of 1000 °C, the surface was brittle and easily friable. However, in other cases, gloss was observed on the surface, and the soil and ash adhered firmly to the test pieces. In all of these cases, the hardness was greater and the water absorption was lower than those of unglazed pieces fired under the same conditions without glaze.
Moreover, this tendency became more pronounced as the firing temperature increased.
No significant differences in properties were observed based on sieve size or elutriation treatment; however, elutriated samples with finer particle sizes showed more uniform glaze coverage.
For the handmade glazes, Mohs hardness ranged from 1-2 to 7-8. In the case of the commercially available transparent glaze, the maximum hardness of 7-8 was observed at 1250 °C, matching the maximum hardness achieved by the handmade glazes. In the water absorption test, the maximum absorption was 20.9% and the minimum was 5.56%. For the transparent glaze, the lowest absorption was 9.23% at 1250 °C.
Okubo (2017) reported that X-ray diffraction of the clay fraction of the SWFS soil revealed that it contains 2:1 type layer silicate minerals such as vermiculite and illite; the 1:1 type layer silicate mineral kaolinite; the iron hydroxide mineral lepidocrocite; and quartz. These clay minerals are likely responsible for the observed variations in hardness and water absorption.
Conclusion
Based on the above results, glaze formation was confirmed by incorporating ash, indicating that the use of SWFS soil as a glaze material is feasible. A ceramics instructor at our school also evaluated the fired results as suitable for use as a glaze. On the other hand, further investigation is needed for the use of SWFS soil alone as a glaze material.
We have been aiming to make “Sagano Yaki” by using residual soil derived from weathered rock in the Sagano High School Woods for Field Studies; hereafter, the soil derived from this site is referred to as SWFS soil.(Nakagawa, 2025). The clay of SWFS is considered difficult for potters to handle because it contains coarse sand fractions and has little silt fraction (Taniguchi et al, 2024). However, Ijiri (2024) analysed the grain size composition and reported that SWFS soil is viable as a ceramic clay, suggesting that its handling characteristics can be regarded as a distinctive property rather than a limitation.
One application of clay materials is in the preparation of ceramic glazes. Glazes created by potters are sometimes made from locally sourced materials such as clay and ash. Since the soil from SWFS can also be used as clay, it is considered that it may likewise be suitable for use in glazes.
The aim of this study is to evaluate the potential of SWFS soil as a ceramic glaze material.
Method
Glazes were prepared using SWFS soil, applied to bisque-fired test pieces, and then fired. The resulting ceramics were evaluated for their physical properties using the Mohs hardness test and a water absorption test, with a commercially available transparent glaze used as the comparison standard.
The test pieces were fabricated by shaping white clay into disk forms with a diameter of 5 cm and a thickness of 1 cm, followed by firing at 800 °C for 6 hours. The handmade glazes consisted of four types of samples made from SWFS soil sieved to particle sizes below 2 mm and 0.25 mm, with and without water elutriation. Commercially available ash was used as a fluxing agent. The mass ratios of soil to ash were set at 5:0, 4:1, 3:2, 2:3, and 1:4, yielding a total of 20 glaze compositions (4 sample types × 5 ratios). For each composition, 0.8 mL of water was added per 1.0 g of the combined soil and ash, and the mixture was applied to the test pieces. The coated samples were fired in a tabletop muffle furnace (Daiken Corporation) and a Rakuraku kiln (Good Electric Corporation), heated at a rate of 20 °C min to target temperatures of 1000, 1100, 1200, and 1250 °C, and held at the target temperature for 14 hours.
The fired products were evaluated using the Mohs hardness test and a water absorption test. The water absorption test was conducted in accordance with the JIS standard method for measuring the water absorption and specific gravity of refractory bricks (Watanabe, 2023). Water absorption (%) was calculated as: Water absorption (%) = [(mass in saturated state - mass in dry state) / mass in dry state] / specific gravity of immersion liquid × 100. Pure water was used as the immersion liquid.
Results and Discussion
When fired using only the SWFS soil or at a firing temperature of 1000 °C, the surface was brittle and easily friable. However, in other cases, gloss was observed on the surface, and the soil and ash adhered firmly to the test pieces. In all of these cases, the hardness was greater and the water absorption was lower than those of unglazed pieces fired under the same conditions without glaze.
Moreover, this tendency became more pronounced as the firing temperature increased.
No significant differences in properties were observed based on sieve size or elutriation treatment; however, elutriated samples with finer particle sizes showed more uniform glaze coverage.
For the handmade glazes, Mohs hardness ranged from 1-2 to 7-8. In the case of the commercially available transparent glaze, the maximum hardness of 7-8 was observed at 1250 °C, matching the maximum hardness achieved by the handmade glazes. In the water absorption test, the maximum absorption was 20.9% and the minimum was 5.56%. For the transparent glaze, the lowest absorption was 9.23% at 1250 °C.
Okubo (2017) reported that X-ray diffraction of the clay fraction of the SWFS soil revealed that it contains 2:1 type layer silicate minerals such as vermiculite and illite; the 1:1 type layer silicate mineral kaolinite; the iron hydroxide mineral lepidocrocite; and quartz. These clay minerals are likely responsible for the observed variations in hardness and water absorption.
Conclusion
Based on the above results, glaze formation was confirmed by incorporating ash, indicating that the use of SWFS soil as a glaze material is feasible. A ceramics instructor at our school also evaluated the fired results as suitable for use as a glaze. On the other hand, further investigation is needed for the use of SWFS soil alone as a glaze material.