素材
Gaffer Casting Crystal
Japanese: Gaffer Casting Crystal
New Zealand-made lead-containing cast glass (equivalent to COE 92). Its viscosity curve shifts toward lower temperatures compared to other types, making it easier to pour into complex molds. This glass offers high transparency and is specifically designed for casting.
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Gaffer Casting Crystal is a lead-containing glass manufactured by Gaffer Glass of New Zealand specifically for casting. It has a COE equivalent to 92 and a lead-silicate (Pb-silicate) composition containing at least 42% lead oxide (PbO). Due to the addition of lead, the viscosity-temperature curve shifts 75–100°C lower than that of standard soda-lime glass (such as Bullseye COE90); consequently, the log η 4–5 (fine flow region) is located around 800–850°C, facilitating glass flow into the fine details of complex molds (§6.2). It is characterized by transparency and optical purity specifically optimized for use as a casting crystal.
Gaffer Casting Crystal is officially defined by Gaffer as having a T⁴ (working point, log η=4) of 902°C, making it ideal for lost-wax casting and precision die casting that require fine detail. However, since it is a lead-containing glass, there is a risk of sulfidation and blackening (Pb²⁺ + SO₃²⁻ → PbS) when combined with refractory gypsum containing sulfates (which applies to many commercially available products). Essential precautions include using lead-compatible refractory plaster (such as Crystalcast) or limiting the firing temperature to 880–900°C. Additionally, as a lead-based glass, safety precautions must be taken when disposing of waste and handling dust.
Physical Data
CTE (20–300°C) 92 × 10⁻⁷/°C. Density 3.6 g/cc, refractive index nD 1.620, Young’s modulus 57 GPa. Transition temperature (Tg) 430°C, strain point 390°C, softening point (T⁷·⁶) 594°C, working temperature (T⁴) 902°C. Casting temperature 780–850°C.
According to the official MSDS, the composition is lead crystal with PbO ≥ 42% (listed as 45% by the distributor, Ebbatch Color).
Product Features
Lead-containing glass designed specifically for casting. Because its viscosity curve shifts to lower temperatures compared to other systems, it flows easily into complex molds, making it suitable for lost-wax and precision casting. Its high refractive index and density provide excellent transparency and optical presence.
The official guideline for soak time is thickness (inches) × 4 hours. The boundaries for the three-stage cooling process vary depending on the thickness range (12–50 mm / 60–138 mm / 150–254 mm).
Country of Origin
New Zealand. Manufactured by Gaffer Colored Glass Ltd. Distributed in the United States.
Related Concepts
Sulfide Blackening ・Refractory plaster, lost-wax casting, the VFT equation, and the η-T-t framework: Use these concepts to understand the physical properties and safe handling of lead-based cast glass.
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.