I would advise against using marbles too. Glass is not really known for being non-brittle. The obvious reason would be the fact that glass does not burn. If you had shards or even fine particles in your fire works there is a posibility of unintended injury. This is where the not burning takes effect, the glass will become a hard peice of shrapnel and more importantly, not burn up like metal. Even if it does not hurt anyone instantly by hitting them hard, there is still the off chance that it will end up in someone's eye. You do not need much to severly irritate an eye. Take the word of anyone who has had metal or glass in their eye. The bad thing is that it take a couple of days before you realise it is there. And by the time starts to hurt, and then you finially decided that it is actually worth going to hospital, it has embedded itself nice and deep. I had three bits of metal in my eye once. It took about two days to become uncomfortable, another day for it to become painful, half a day to decide I need to go to hospital, and then half an hour in Ashford Hospital's eye clinic. Only one of the bits was only just visable to the naked eye. The other two were microscopic. It would have been really nice if it took five minutes to recover, but it took about three months before my eyesight was back to normal. I'm not a H&S junkey myself, I'm not trying to belittle anyone by giving the school style eye talk, just advising safer methods to practice. I personally use ceramic media for all my milling. It is very very hard and any dust that might be produced is inert. Hardened metals are also good, because the bits will burn up when the composition burns, but the down side is posible contamination.
Edited by Andrew, 19 February 2005 - 06:34 PM.