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Old 12-01-2018, 02:09 PM
Bradley Howes Bradley Howes is offline
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Location: Palo Alto, CA
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Black Calcedony

Hello All,

I've been using a modified version of Pete's calcedony to do some research into calcedony. I'm currently an undergrad at Alfred University with Angus Powers as my teacher. I'm taking Glass Art Engine, a class that brings artists and engineers together to find 'problems' in glass that we want to work on.
For those who don't know, Pete's calcedony is:
8 lbs cullet
4.6g silver nitrate
28g black tin oxide
28g zinc oxide
2g red iron

I'm using 75% of the silver, 7g red copper oxide, and about 100g sugar for some reduction.
About 50% of the time, the glass is black with a few cords of color. My very first run of calcedony looked like it was dipped right out of one of Josh Simpson's crucibles. When it turns out black, I'll weigh out about 25% more oxides and throw that on top of the pot and mix it in with a punty. After 30-60 mins, the glass is a lot better but still not great.
I understand calcedony is a fickle color but I'd like to know if there's anything I can do to influence it in future melts.
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