設計・制御
Peak Hold (Stage D)
Japanese: 最高温度キープ（D段階）
Stage 4 of the firing program. This stage involves holding the piece at the target (peak) temperature to complete the melting and shaping of the glass. The combination of holding time and temperature determines the final shape.
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Peak Hold (Stage D) is the fourth stage of the eight-stage firing program; it is the phase in which the glass is held at the target temperature (peak) to complete the fusing and shaping process (§8.1). In η-T-t trajectory notation, this corresponds to “peak hold.” The final shape of the glass is determined by viscous flow during this stage. The standard hold time is 10 to 30 minutes for full fusing (780°C) and, for pot melting (820°C), a time calculated based on the weight of the contents (soak = max(20, weight [g]/100 × 6) minutes) (§12.4).
The combination of peak temperature and holding time during Stage D is the most critical parameter determining the final shape, and it also involves a trade-off with the risk of loss of transparency. Higher temperatures and longer holding times promote glass flow, allowing for the completion of fine details and shape changes, but they also increase the risk of prolonged residence in the loss-of-transparency zone. The “calibration test for each electric furnace” (3 cm square × 2 layers stacked × 5 points) recommended by Rei Chikaoka (2021, p. 157) is an experiment designed to determine the actual temperature distribution during Stage D. Incorporating furnace-specific variations into the Stage D temperature settings forms the foundation for high-precision production.
Related Concepts
Rapid Heating (Stage C) (firing-stage-c) · Rapid Cooling (Stage E) (firing-stage-e) · Full Fusing Zone (full-fusing-zone) · η-T-t framework (η-T-t-framework) and the VFT equation (VFT equation) to understand the physical basis of peak design.
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.