Tumbling copper is needed to force the cleaning oxide against the glass for polishing. The normal is cut from new 12 gauge wire into 3/32" and 5/32" lengths. Fine is also available which is cut from new 14 gauge wire into 1/16" length. Several mediums have been tested for cleaning including buckshot, aluminum wire, BB's, glass beads, sinker pellets, etc. and so far copper has proved to be the best. Unfortunately it is somewhat expensive. However, once purchased you will have the necessary amount and will only need to purchase small amounts as the copper wears down and this will be seldom in that the copper is completely reusable.
To determine the amount you will need, you can use the following formula:
1) Determine the number of canisters you intend to turn at one time
2) Total the largest combination of canister sizes that could turn at one time
3) Multiply this total by 4 and add 5
This will give you the minimal amount of copper necessary for your needs.
For example, if you purchase a two canister system with a 4" and a 6" canister, you will need: (((4 + 6) * 4) + 5) = 45 pounds.