Hey I might have found something that could help you and I out.
I just came across an investment called mold mix 6. They claim free of haze! It is not your typical cheap plaster/silica flour mix. This one is alumina fibers and alumina powders and even capable of tolerating bronze. It is not cheap, but neither is my time! I'm trying bandust one more time with Gaffer glass and if this doesn't work, I'm chucking that 50lb box of investment in the TRASH!
If anyone has any thoughts about mold mix, I'd be thankful if you could share your experience with this stuff. Thanks!