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Rocks are usually polished using a rock tumbler. The fundamental procedure is to tumble the rocks with increasingly finer or prime grits and polish until the appropriate shape and shine is attained. This procedure generally takes 5 to 6 weeks to finish a cluster.
Here is a video tutorial on how to polish rocks in a tumbler:
You can follow the procedure below on how to polish rocks in a tumbler by using either rotary tumblers or vibratory tumblers.
Rotary Tumblers
If you are tumbling for the first time, you should also consider the place where you would do the process. Tumblers with rubber or metal barrels produce noise and there's also a possibility of barrel leaking. Therefore, choose a location where leaks and noise wouldn’t be a problem.
Choose rocks that have approximately the same level of hardness without any cracks. A blend of sizes between 1/2" to 1" is best for a right tumbling action. Keep a record of your every action for future reference.
1.Load the barrel with the rocks you've chosen.
If you don't have sufficient rocks, use plastic pellets to fill the load. Add abrasive grit to the tumbler. Use up to 3 tablespoons for one pound of load.
Spray this on your load and then gently add some water and close the barrel. Also check if there is any leak. The main aim of this step is to obtain well-rounded rocks. If this is not attained in 10 days, then repeat the step with fresh grit.
2. Load the cleaned rocks into the barrel again followed by fresh grit and water.
Also make sure that the mixture is a little thinner than the previous one. The main idea of this step is to ground all the scratches, producing an even finish. This step would take approximately 10 days to complete.
3. This also known as the pre-polish stage.
Add the whole mixture to the tumbler as we did in step one and two. Also note the consistency and progress of the slurry every day.
After a week, test one of the rocks by rubbing it with a piece of paper or a towel. If the surface of the rock doesn't get a clear shine on it, repeat processing.
4. Add polish compound followed by water.
In this step, you must be very careful when loading the rocks into the barrel. If you didn’t use plastic pellets, then use them in this step because they hold the polish compound well.
Vibratory Tumblers
Like the rotary tumblers, these too are very noisy so it’s best to place them on a carpet. Here you can choose any rocks of your choice and load them to the hopper.
1. Load the hopper with the rocks that you have chosen.
Add up to 2 tablespoons of grit for one pound of load, and water in the hopper. When the rocks get tumbled a thick slurry is formed. Check every few minutes and keep on adding water. The main idea of this step is to attain rounded rocks.
2. Place the cleaned rocks in the hopper followed by fresh grit and water.
Try to check it frequently. The aim in this step is to obtain a smooth finish. This may take up to 4 days. When you are pleased with the result clean the rocks and hopper completely.
3. Load the hopper as you did in the first two steps and continue the procedure.
Check the slurry frequently. This step will be completed if you notice a dull gloss after rubbing a rock with a towel or paper.
4. Use 600 grit aluminium oxide.
This step is optional. It is also known as the pre-polish step. This helps in attaining nice rounded rocks. All other directions are same as previous steps. Process it for at least 2 days.
5. Load the hopper with the same mixture and add polishing agents.
This step is also known as the polish step. Perform this step for up to 4 days and clean everything completely.
Both types of tumblers are effective to use and it is up to you to choose which one to use on how to polish rocks in a tumbler.
References:
http://www.mamasminerals.com/How-To-Polish-Stones-with-a-Rotary-or-Vibratory-Tumbler_ep_147.html
http://rocktumblingsupplies.com/faq.phtml
https://www.youtube.com/watch?v=TYp-OzlPzeQ
http://www.gemworld.com/tumbling.asp
http://chemistry.about.com/od/geochemistry/fl/Rotary-Rock-Tumbler-Instructions.htm