温度・粘度
Viscosity Zone Map
Japanese: 粘度領域マップ
A chart listing log η values alongside temperature ranges, phenomena, and corresponding techniques. It provides an at-a-glance view of what happens in each temperature range and serves as a guide for firing design.
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A Viscosity Zone Map is a chart that lists, with the viscosity range of glass (log η) as the axis, the temperature ranges corresponding to each viscosity zone, the phenomena that occur within those ranges, and the corresponding kiln-working techniques (Treatise §3). This map provides an intuitive understanding of “why and to what temperature the glass should be heated.” The main viscosity zones and their corresponding characteristics are as follows: log η > 14.5 (below the strain point, <450°C) corresponds to a fully rigid state with a risk of thermal shock; log η 13–14.5 (450–520°C) corresponds to the annealing zone, where stress relief is possible; log η 9–13 (520–630°C) corresponds to viscous flow, self-weight creep, and slumping; log η 7.6–9 (630–680°C) corresponds to tack fusion and pattern transfer; log η 6.6–7.6 (680–720°C) corresponds to softening and full fusion; log η 4–6 (720–850°C) corresponds to flow, casting, and lost-wax processes; log η 2–4 (850°C and above) corresponds to low-viscosity flow and pot melt.
The viscosity region map becomes more practical when interpreted in conjunction with the four-zone classification (I: Do not break / II: Do not leave distortion / III: Do not stain / IV: Beautiful). If the four-zone classification serves as a framework for “what to pay attention to,” the viscosity region map provides the physical basis for “what happens at what temperature.” It is helpful to keep this in mind as a conceptual map of the η-T-t framework and as foundational knowledge when designing firing programs.
Related Concepts
粘度-温度曲線（viscosity-temperature-curve）・粘度定点（viscosity-fixed-points）・4ゾーン（four-zones）・η-T-tフレームワーク（eta-t-t-framework）・軌跡言語（trajectory-language）
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.