温度・粘度
Bubble Squeeze Zone
Japanese: bubble squeeze帯
Temperature range of 660–680°C. This is the holding zone for an intermediate process in which viscoelastic forces expel air bubbles from the glass. There is a high risk of devitrification, so Bullseye recommends holding for no more than 30 minutes.
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The bubble squeeze zone is the temperature range between 660 and 680°C, during which the “bubble squeeze” (§7.2) process occurs in fusing and pot-melt firing, where air bubbles trapped between layers of glass are pushed toward the outer periphery through viscoelastic flow. In this zone, the glass begins to soften, allowing air trapped at the interfaces to be efficiently expelled. Bullseye recommends a maximum hold time of 30 minutes; exceeding this time causes the risk of loss of transparency to rise sharply (§12.1).
The reason for the high risk of devitrification is that the temperature range of 660–680°C overlaps with the range where crystalline phases such as devitrite (Na₂Ca₃Si₆O₁₆) are prone to precipitation. Prolonged dwell time causes iridescent wrinkles or cloudiness to appear on the surface. In the firing program, the basic strategy for avoiding devitrification is to quickly pass through this temperature range during the C stage (rapid heating) and the E stage (rapid cooling), and even when designed as a “bubble squeeze,” to limit the duration to within 30 minutes. Awareness of this temperature range forms the core of Rei Chikaoka’s (2012, 2021) four-zone classification, specifically “Zone III (Do Not Stain).”
Related Concepts
bubble squeeze (bubble-squeeze) ・Rapid cooling (Stage E) (firing-stage-e)・Rapid heating (Stage C) (firing-stage-c)・Surface crystallization (surface-crystallization)・η-T-t framework (eta-t-t-framework): Understand temperature design to prevent devitrification in conjunction with these factors.
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.