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One of the most amazing characteristics of polymer clay is that it can be sanded and buffed until it looks almost like glass. But all that sanding is hard work on the hands and fingers! Here are easy instructions on sanding beads using an inexpensive rock tumbler found in the kid's section at the craft stores.
This method uses wet/dry sandpaper. Using an old pair of scissors, cut the paper into strips, then into squares. The squares should be approximately 1 cm square-- if they are much larger, you will find that the paper will curl inward when it is wet, preventing sanding. I would say I cut a loose heap of about 1/3 - 1/2 C of squares.
Next, measure the inside of the barrel on your tumbler. You will want to cut a strip of sandpaper to line the barrel. Cut the width a little shorter so that it does not quite reach the lip of the barrel, otherwise the paper may prevent a tight seal when you put the lid on the tumbler.
I use good old duct tape to tape the sandpaper strip together before fitting it into the barrel, usually a couple of pieces overlapping; that way if one should not hold well, the other will help it. REMEMBER the rough side is on the INSIDE of your sandpaper tube. Pop the tube into the barrel.
Next, place 1/2 your beads into the tumbler, then 1/2 your sandpaper squares, the rest of your beads and the rest of your sandpaper squares on top. Don't fill the tumbler more than 3/4 full, otherwise there won't be enough room for movement and things won't tumble and sand nicely.
Now its time to fill the tumbler with water. Fill it so that the water just covers your beads & sandpaper. Too much water prevents the beads from tumbling, they will just float around in the barrel. Remember, you want them to rub against the sandpaper sides and the squares in the water so that they get sanded. Add a drop or 2 of liquid dish soap. Not too much, or you'll wind up with bubbly water! (I've never heard why to put in the liquid soap, but any instructions I've read about using a tumbler suggest it-- if you know why, please leave a comment).
Finally, use vaseline/petroleum jelly around the outside lip of the tumbler and the inside edge of the tumbler's lid to act as a seal. Be careful not to use too much, as too much may ooze into the tumbler and make your beads feel tacky and they will be more difficult to buff later. Twist on and lock the lid and check your seal for leaks. All good?
Then its time to tumble! I start with 400 grit paper and let beads tumble for about 16 hours. Then I switch to 600 hundred grit, same amount of time. Depending on how smooth you want your items to be, you can continue with smaller grits until you are satisfied with the look & feel of your beads.
But WAIT-- don't throw away all that sandpaper! I've found that it can be dried and used at least one more time. So spread it on a towel to dry and use again. The duct tape should be fairly easy to pull off the strip lining the tumbler. You may need to lie something on top of the strip that lined the barrel so that it will dry flat.
This is only one method for using a rock tumbler for sanding your polymer clay pieces. I've heard there is some sort of technique using a tumbler & river rocks to sand polymer and I've heard rumors that you can also buff beads using a tumbler filled with felt. If you have any experiences with using a tumbler for your polymer clay, please share in comments!