You can melt glass at 1650 F that is cone 06. if you fire to cone 6 and above some of the reds and yellows may burn out. go for it though i am not here to tell you what you can't do. if you do have something that suspends over something else (like a lidded jar) do not put a ton of glass in it the lid, it will melt through the clay and down into the jar. The glass will crackle no matter what you do but modern dishwashers and microwaves and ovens will clean/kill any bacteria that can get into the crackles. when you put glass into something use a bit of school glue to help hold the glass in place. it really helps when you load a kiln and you don't have to worry about spilling your glass shards all over. good luck!!