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Old 05-30-2019, 06:40 AM
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Pete VanderLaan Pete VanderLaan is offline
The Old Gaffer
Join Date: Apr 2002
Location: Chocorua New Hampshire
Posts: 21,324
Pete VanderLaan is on a distinguished road
A basic observation on old pots: They have tons more surface area exposed to the melt than new ones do. A new pot looks quite smooth, even magnified. An old one looks like a chart of a 7.5 richter scale earthquake. The amount if interaction is really large and will absolutely affect a melt.

I do not drop to 1900F at all. 2000F is as far as I go these days. Sometimes I stay nearer to 2050. The glass tells me what it wants.
The antimony remains in the melt. It doesn't gas off. It performs a function of valence switching wherin the antimony takes on electrons in the outer electron ring. It goes back into solution. Going to the squeeze too fast makes that more difficult as the viscosity of the glass goes way up. Glass really doesn't lke to be hurried and actually doesn't do well with schedules. I prefer proofing and having the glass visually tell me what it's doing. The bubble size sounds right but really fine bubbles indicate a melt that is not yet chemically complete, or of some external factor adding to the soup, like an old pot.

As has been noted, don't ever add batch on top of unmelted batch. Confirming your thermocuple's accuracy might be appropriate. The more stirring the better as long as the melts are complete. Otherwise, stirring unmelted batch down in the pot may melt poorly, having been insulated.
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