My tumbling rules, sort of....
Well, I am not a mega tumbler but I use to do tumble polish about 100 pounds a week to sell at shows. It paid the overhead while I sold cabochons and jewelry. Also kept the kids busy while I spoke with mom and dad. Dry tumbling sounds interesting. How do you clean the rock with no water in the building???? intrigued I am
I never mix agates, jaspers and rocks of different hardness in the same load. You can do it and still get a nice polish, most of the time.
I rarely use media, almost never!!! I keep a bucket of small jasper pieces, about pea size, to add to the larger rocks being tumbled. The little pieces of jasper make certain the grit gets everywhere and grinds all the fresh tumble pieces from edge to edge. As a bonus you get some really nice small tumble pieces for decoration and to sell to crafters. I do the same for agates. Most instruction books say to use a mix of small, medium and larger chunks in any load of tumble rock. You have to have tiny pieces in the mix or use media. I choose tiny, it is a win - win....
I make certain to run the tumbler, rotary or vibratory, long enough for the grit to break all the way down. 7 days per grit on the rotary, usually 3 days per grit on the vibratory. I never use any grit higher than 500 in my vibratory tumbler so the barrel will last. On really rough rock I run the tumbler twice with 60 / 90 grit or else I rough off the hard edges with a 60 grit diamond wheel.
Thanks for the link to tumbling obsidian..............