温度・粘度
Full Fusing Zone
Japanese: フル域
A temperature range of approximately 780°C (COE 90). This is the temperature range at which the glass fuses completely into a single, flat sheet. The surface becomes uniform, and the layered parts fuse completely to form a single sheet.
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The full fusing zone is the temperature range around 780°C (based on Bullseye COE 90), within which the glass fuses completely into a flat, unified mass (§8.2). In terms of viscosity, this corresponds to log η 5–6 (Pa·s); once the Littleton softening point (log η = 6.6) is exceeded, the glass enters a state where it can be completely deformed under its own weight. The layered parts fuse completely due to surface tension and their own weight, and the surface is uniformly flattened to form a single sheet of glass. Edges and cut surfaces disappear, and the surface becomes smooth.
In the temperature range where “full fusing” occurs according to Reo Chikaoka’s (2012, 2021) five-stage fusing classification, the value of 780°C is the standard for Bullseye COE90. Since the full-fusing temperature range varies by glass type (OYF shifts toward lower temperatures, while Effetre Murano shifts toward higher temperatures), it is recommended to measure your furnace’s actual full-fusing range using a calibration test (two 3 cm square pieces stacked on top of each other, arranged at five points) when using a new electric furnace or a new type of glass. The standard peak hold time is 10–30 minutes; the longer the hold time, the more the curve flattens.
Related Concepts
Gain an understanding of the entire fusing temperature range, including the tack zone, block-press zone, full fusing, plate-count effect, and η-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.