And I use 2 pounds of stainless steel shot that has a mixture of shapes. I think the little pin shapes are important for getting into tight spaces, but some people say they leave little marks on flat pieces (I've never had that problem). Stainless steel is good so that it doesn't become a rusty mess, and I think the easiest way to store it is in water.
So I pour my shot into a sieve and then pour it into the tumbler barrel. Put your jewelry pieces in and add water so that it just covers the shot.
Everyone has their own favorite burnishing agent. Dawn is popular, but I think you have to use the original Dawn, which is really hard to find. You can also purchase burnishing compound. I personally like to use flakes of Ivory soap. I just use a cheese grater to shred it into a container so I have it on hand. I put in probably something around 1-2 tablespoons of shavings.
Now making sure that the lip of the barrel is dry, fit the inner lid so that it sits snugly into the barrel. If the area where these two pieces touch is wet, you're not going to get a good seal, and you'll most likely have leaking.
The washer goes on next, and then twist the little nut on. Not too loose, or it will work its way off, but not too tight or it will distort the inner lid and break the seal.
That's it! You can tumble for any length of time, depending on what you're tumbling and what you're trying to accomplish. I tumble almost everything overnight. Then you just drain your shot and admire your jewelry!
So here's an earring that's done. It's hardened the ear wire portion so that it's still flexible but not flimsy, and gives the whole piece a nice polished, smooth look. It's especially nice for my hand-sawn pieces so that the edges are perfectly smooth.
Tumbling is NOT a final step and is not going to do major finishing work or take out scratches. It WILL harden your pieces, give them a nice shiny glow, and make your jewelry look better. After tumbling, I do my final finish on the piece. I use progressively finer grits to sand them and then progressively finer polishes. If the final piece is to be shiny, then I'm done. If I want to do a matte, satin, or brushed finish, that actually happens after I bring the piece to a decent polish to be sure that there are no scratches. Just because a piece is brushed doesn't mean I want a scratch lurking in there!
Definitely a must-have for any jewelry studio. :)