Interesting....I have saved glass and pottery for years (folks who didn't know will think me crazy if I die and they find it all broken in boxes in the basement...but oh well, no worry what they think then anyway!) Because I managed during my working years in a manufacturing facility that made Harley and John Deere parts (amongst others), we had many large tumblers. We did some tests on tumbling glass for me when there was opening on the machines and found that sand was not the best first media. The shop manager used a larger media and we had beautiful results. I quit that job before I knew more but, with the manufacturing recession right now I would suggest that it might not be a bad idea to check machine parts manufacturers as a resource for knowledge and service.
