温度・粘度
Surface Crystallization
Japanese: 表面結晶化
A type of opacity in which the opacity originates at the glass surface and spreads outward. Scratches, dirt, grease, and gas from release paper are common sources of these opacity nuclei. This is the predominant form of opacity in pâte de verre.
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Surface crystallization is a form of crystallization that occurs during the devitrification of glass, in which crystal nuclei form and grow from the glass surface rather than from within the glass (§7.3). If the glass surface is rough, or if foreign substances—such as oils, dust, gases from release paper, or moisture from refractory plaster molds—are adhering to the surface, these substances act as nucleation sites, causing crystalline phases such as devitrite (Na₂Ca₃Si₆O₁₆) to spread from the surface. This concept is contrasted with bulk crystallization (internal nucleation).
Basic preventive measures during production include removing grease and dust from the surface with rubbing alcohol (Chikaoka 2021, p. 7, p. 160), thoroughly wiping away any foreign matter—such as pencil marks—before firing, and checking the condition of the release paper. In Pâte de Verre, surface crystallization is the dominant form of opacity loss due to the very large specific surface area of the glass particles. In glass systems with a low sc-sinterability parameter (Sc), surface crystallization is likely to occur, resulting in a high risk of opacity loss. Rapid heating (Stage C) and rapid cooling (Stage E) to quickly pass through the decolorization danger zone are the primary strategies for preventing surface crystallization.
Related Concepts
Sinterability parameter Sc (sc-sinterability) and bubble squeeze zone (bubble-squeeze-zone) ・Gain an overall understanding of the devitrification mechanism in conjunction with rapid heating (Stage C) (firing-stage-c), rapid cooling (Stage E) (firing-stage-e), and the η-T-t framework (eta-t-t-framework).
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.