Borosilicate Glass

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Borosilicate glass is a type of glass that contains boron trioxide (B₂O₃) as its primary component; its most distinctive feature is its low coefficient of thermal expansion (equivalent to COE 33, α ≈ 3.3 × 10⁻⁶/K) (Treatise §1.2). Representative products include Pyrex (Corning; currently manufactured by Schott under the DURAN brand) and JENA GLASS. Due to its low coefficient of thermal expansion, it is resistant to sudden temperature changes (high thermal shock resistance) and is widely used for scientific and laboratory equipment, heat-resistant tableware, and laboratory glassware. In lampworking, it is highly popular as borosilicate (also known as “boro”).

It is important to understand that this glass is “generally unsuitable” for kiln work (fusing, slumping, and casting). There are two reasons for this: (1) Because its COE differs significantly from that of soda-lime glass (such as COE 90), mixing it with SLS-type glass will cause it to crack due to differences in thermal expansion. (2) Since its softening point and annealing point are more than 100°C higher than those of SLS-type glass, the degree of shape change is insufficient within the typical kiln-working temperature range (700–850°C), and fusing will not occur. While kiln work with other borosilicate-based materials is possible in a high-temperature kiln, it requires a setup that is completely different from that used by SLS-based users. When a lampworker asks, “Can I fire this low-quality material in a kiln?” the answer is usually, “Separate equipment is required.”

Related Concepts

ソーダ石灰カリガラス（soda-lime-potash）・COE（coe）・粘度-温度曲線（viscosity-temperature-curve）・ガラス転移（glass-transition）・VFT式（vft-equation）