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I'm. making a 30 inch x 40 inch 9mm thick panel what should the anneal time be? I thought about 12 hours would that be enough

Bullseye would say about half that, or less. http://www.bullseyeglass.com/methods-id ... slabs.html

They don't have 9mm in their chart, so to be conservative go with 12mm or even 19mm, which are still below 12 hours.

Michael Stevens wrote:I'm. making a 30 inch x 40 inch 9mm thick panel what should the anneal time be? I thought about 12 hours would that be enough

I anneal 10mm float with a 1.2 hour soak at 1000, 1.2 hours down to 900, .8 hours down to 700, .8 hours down to 300. For fusing glasses, I drop those temps down 80ºF. A twelve hour soak would insure the glass would be the same as the kiln, from edge to edge. In most kilns that would insure annealing impossibility. You really can anneal soak too long. The temperature near the walls isn’t the same as in the center. Annealing actually takes place in about 15 seconds when the entire mass of glass is within 5ºC inside the annealing range, no matter what size the glass is.

If our thickness isn’t uniform, I might extend to 2 hours soak, from 1.2 etc.