素材
Soda-Lime-Potash Glass (SLS)
Japanese: ソーダ石灰カリガラス
The primary composition system for kilnwork glass, consisting of Na₂O, CaO, K₂O, and SiO₂. Most art glass, such as Bullseye, A-Ski, and OGT, belongs to this system.
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Soda-lime-potash glass (SLS) is a glass system composed primarily of sodium oxide (Na₂O), calcium oxide (CaO), potassium oxide (K₂O), and silicon dioxide (SiO₂) (treatise §1.2). Most art glass used in kilnwork (such as Bullseye COE90, Oceanside System 96, A-Suki, OGT, etc.) belongs to this composition system. The glass transition temperature (Tg) ranges from 480 to 510°C depending on the type, and it has a viscosity-temperature curve suitable for a wide range of techniques, including fusing, slumping, and casting.
When using SLS as a reference system, it is easier to understand the shift in viscosity curves caused by differences in glass composition. For high Na₂O/K₂O systems (such as Effetre Murano with a COE of 104), the viscosity curve shifts approximately 40°C lower than that of SLS, making the glass softer at the same temperature. PbO-based systems (such as Gaffer Casting Crystal, 42%+PbO) shift even further to the lower-temperature side by 75–100°C. Borosilicate systems (such as Pyrex) are, conversely, positioned more than 100°C on the higher-temperature side and are unsuitable for kiln work. The author’s (Rei Chikaoka) proprietary OYF blend also belongs to the SLS group, but due to its unique formulation, its slow-cooling point is estimated to be lower than that of the Bullseye series (Tg ≈ 460°C).
Related Concepts
COE（coe）・VFT式（vft-equation）・ガラス転移（glass-transition）・粘度-温度曲線（viscosity-temperature-curve）・Bullseye COE90（bullseye-coe90）・OYFガラス（oyf-glass）・ホウケイ酸ガラス（borosilicate-glass）
This entry is written in Japanese by Rei Chikaoka and translated for readers outside Japan. If something reads oddly, the original is the source of truth.