Glass-Cast 910 / 965 (R&R)

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Glass-Cast 910 / 965 (R&R Glass-Cast) is a refractory plaster specifically designed for glass casting, manufactured by Ransom & Randolph (R&R) in the United States; it is the industry standard most widely used by kiln workers in North America (treatise §10.4, §15.1). 910 and 965 are product numbers within the series, and their properties—such as water-to-mix ratio, setting time, and shrinkage rate—differ slightly. Common characteristics include: high heat resistance (withstands temperatures of 900°C or higher), low shrinkage, consistent mold surface quality, and a wealth of practical experience and technical documentation (including numerous publications on its use in combination with the Bullseye TipSheet).

It is important to note that Glass-Cast 910/965 ** sulfates (CaSO₄-based) as their main component**; therefore, when combined with lead-based glass (such as Gaffer Casting Crystal), they may release SO₃ at high temperatures (900°C or higher), posing a risk of lead-crystal blackening. For this reason, it is important to distinguish between Crystalcast M248 (which is also available in a sulfate-free version) and lead-free alternatives. Problems are unlikely to arise when used in combination with lead-free glass (such as Bullseye or Oceanside). Since this product is available in Japan only through import agents, you should also consider comparing it with domestic products such as G-2 Noritake (g2-noritake) and C-2 Yoshino Gypsum.

Related Concepts

鉛クリスタル黒化（lead-crystal-blackening）・Crystalcast M248（crystalcast-m248）・Bullseye 50/50（bullseye-50-50）・近岡式耐火石膏（chikaoka-plaster）・耐火石膏（refractory-plaster）・耐火石膏予熱（predry）