To tell if a stone is soft, scratch it with another rock. If the scratch looks chalky, the stone is soft. Also try to pick a rock with a roundish shape, without major protrusions or indentations.
If you are happy with the shape of your rock, don’t worry about shaping it. You can also rub the stone over a slab of concrete to break off any protrusions.
Make sure not to buy colored polish, or it may stain the stone.
A cheap, plastic tumbler is a good option if you only want to use it a few times. Spring for a more expensive tumbler if you can see rock polishing as a new hobby.
You don’t want to put rocks of different hardness in the tumbler because the harder rocks will wear down and scratch the softer rocks. You also don’t want to put in differently shaped rocks, with some being jagged while others round, because the rounder rocks will get polished faster than the irregular rocks. Try to put in rocks of various sizes. This will help the rocks achieve a more uniform shaping. You can use a cabbing machine if they are dome top, flat bottom Cabochons. Use a flat lap or lapidary wheel for faceted stones.
Tumble the rocks for 3 to 7 days, checking every 24 hours to make sure that everything is going smoothly. The coarse grit is meant to smooth out the shape of the rocks. For rounder rocks, it should only take about 3 days to get a nice shape. For more jagged rocks, it may take about 7 to even the surface out. Checking every 24 hours lets you see the progress of the rocks. After checking, you may decide that either they are ready for the next step, or that you want to keep tumbling them for another day.
Thoroughly wash your rocks and the tumbler until they are spotless. Having even small amounts of coarse grit left over can disrupt the next part of the process.
After four or five days, stop the machine and open it up. Place the rocks in a container and clean out the grit. Again, make sure that the rocks and the container are completely clean, and throw out the grit instead of flushing it away. [4] X Research source
This is the last stage of using grit, so don’t cut the cycle short until you are happy with the smoothness and shininess of the rocks. You may need to clean a rock off to see the shine when you’re checking in on the progress of the rocks.
