I have established a formulation for a dual-purpose glass which appears to be great for both blowing and kilnforming applications. A dual purpose glass will facilitate the complete integration of hot-working techniques in art glass applications. Spruce Pine 87 shows appreciable devitrification after only a single firing in kiln-casting applications. Other commercially available batch glasses are marginally better than Spruce Pine 87, but tend to devit on the 2nd or 3rd firing.
The new formulation appears to be fully compatible with Spruce Pine 87 batch, and capable of multiple firings in kiln applications with minimal devitrification. Of the Reichenbach and Gaffer colors tested so far, all were compatible in blown pieces, but some appear to be incompatible in castings. The batch showed some stress (polarized light) with System 96 glass and with glass from Gaffer batch. I hope to optimize the batch with the help of Gaffer, as they offer trident-seal testing. They also trident-seal test their color batches as part of their production process.
The batch was produced with a common silica source and without decolorizer; its relatively colorless and suitable for thick applications. The addition of 0.1% fining agent was sufficient to fine the glass; additional work will continue to further reduce this component. The batch melts/cooks at typical temperatures (1230-1290 C or 2250 – 2350 C). Materials are commonly available from pottery supply companies, and cost roughly $0.55 – $0.65 per pound. A rotary cement mixer was used to mix the batch in 60 kg quantities; its poly drum has been fitted with a simple lid to keep to contain the dust. The batch can be pelletized in the mixer with a sodium silicate solution.
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