# Rock Tumbling Instructions
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Stone Selection
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Rocks ideal for tumbling usually have interesting colors and patterns. Selections can be sorted based on size, color and hardness. After tumbling, rocks will lose approximately 30 percent of their size. Hardness can be determined by using "Moh's Scale of Hardness," which rates hardness based on the scratch resistance of the mineral. Prior to an initial tumbling, rocks should be placed in small, medium and large groups according to their size.
Rough Grinding
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Rough grinding is the initial step on the route to professionally polished rocks. Clean rocks are placed in the barrel of the tumbler. Grit is then added along with baking soda. Water is poured over the rocks until they are covered. The tumbler is checked for leaks and the machine is turned on. Rough grinding lasts for about seven days or until the rocks have a slightly frosted appearance when dry.
Medium Grinding
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Medium grinding removes deep scratches from rocks. Rocks are reloaded into the barrel and tumbled for another seven days. At the end of the week, rocks are tested to see if they have a smooth, frosted look. Rocks and tumbler are then thoroughly cleaned. All grit is removed and any broken or pitted rocks are thrown out.
Fine Grinding
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Fine grinding removes small scratches and imperfections. This is also called the pre-polish stage. Rocks are gently placed back into the tumbler. A pre-polish compound and small amount of sugar are poured over the rocks, along with more water. The tumbler is run for 10 days. At the end of fine grinding, rocks should have a matte finish free of pits and scratching.
Polish
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The last stage in rock tumbling is polishing. Polishing adds a glossy shine to the rocks. Rocks with imperfections such as chips or breaks are removed and the remaining group is placed in the tumbler. A compound such as tin oxide is then added to the barrel along with water for one last spin. The tumbler runs for seven days. When rocks exhibit a glossy sheen, the tumbling process is complete.
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