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John I would check out the second item i.e. one part alumina hydrate or bentonite could this be a mistake? as the alumina h' is refectory. and bentonite (volcanic ash) be is a very plastic clay that's would bind the sand.. so I would say the bentonite may a sub for the kaolin .. but I could be wrong...

And what glass would you be using ? when I use Gaffer Pb crystal if will start flowing at just over 825C from this point to the full flow temperature of 850c I slow the heating rate down Colin