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Rock tumbling is a technique by which rough rocks are made smooth and polished. Rock tumbling is a popular hobby in the United States and other Western countries, and is also done on a larger scale to produce mass amounts of fine polished stones for resale.
The process involves taking rough rocks, often of no real monetary value, and placing them in a special tumbling device. The rocks need to be of roughly the same hardness, so that they don’t destroy each other. Some sort of grit and a lubricant are then also added, and the process of tumbling can begin. Usually rock tumbling takes just over a month, and is separated into four or more different stages.
At each stage of the tumbling, the rocks are subjected to an ever-increasingly fine type of grit. At the beginning stage, the rock tumbling would use very rough grit, to get the roughest edges off of the stones. Next, the rocks will be washed and a finer grit will be added, to begin polishing them. Next, a very fine grit will be added, to get the last of the edges off of the stones. Lastly, after washing, the rocks are placed in with a polishing agent, such as cerium oxide, and some sort of cushioning agent, usually plastic pellets.
One of the difficulties of the process is getting the rocks shaped the way you want them. This can mean tumbling them far longer than you would expect, to try to wear them down. It can also mean manually carving them, in a process known as preforming. In preforming, the stones are cut down to be roughly the shape you want the finished stone to be. If preforming is used, the roughest stage of grit can be passed over altogether, making the tumbling a three step process.
There are any number of stones which can be used, but generally people look for stones that are quite cheap, have striking colors, and have visible occlusions to turn into interesting streaks in the polished stones. Moss agate is one of the most popular stones for rock tumbling, because it has a deep green color with blue and white streaks that makes it visually very appealing. Carnelian is also very popular, with rich browns and reds that complement the greens and blues of moss agate.
All sorts of strange and exotic stones may also be used in rock tumbling, with an emphasis on those that had the oddest shapes within them. Turritella limestone, for example, is popular among hobbyists, since little bits of shell make for amazing and intricate patterns within the polished stone.
To get started in this hobby, you’ll want to find a basic rock tumbler, of which many different affordable models are available. You’ll then get a few different replaceable barrels for the tumbler, one for each level of grit you’ll be using, three different grains of grit, and some liquid polisher. Within a month or so you should have your first batch of finely polished stones, and may have found a new, and surprisingly addictive, hobby.
I'd have to say the results of rock tumbling can be pretty spectacular. I also had one of those kits as a boy and I followed all of the instructions to the letter. Some of the finished rocks looked like pieces of glass. I gave most of them away to my classmates during show and tell, but I made a necklace for my mother with a few of the nicer stones.
I had a rock tumbling kit when I was a child, but I could never get the rocks to become truly polished. One problem I discovered is that the container must be tightly sealed. Sometimes the grit and water would leak out because the lid was not properly threaded. If the water leaks out of the tumbler, it won't work very well.
The other problem I had was the noise of the rocks as they tumbled. It wasn't especially loud, but it was constant. Everyone in the house could hear the crunch as the rocks tumbled in the container 24 hours a day. The motor that turned the container also made a grinding noise. I'd suggest finding a remote location where the rock tumbler can operate undisturbed and the noise does not carry into other parts of the house.