My Rock Polishing Process

McDougall’s Rock Tumbling Process

mcdougallshome.net

I’ve been asked several times about the process I use to polish rocks. Rather than trying to remember the details every time I am asked, I decided to make this document of the process.

Tumblers

I use two types of rock tumblers for the different stages. For this document, I will explain how I use a “run of the mill” rotary tumbler, and a “Lot-O-Tumbler” vibratory tumbler.

I have a Thumler A-R2 dual 3 lb barrel tumbler. There are several brands of tumblers that have two barrels with a capacity around 3 pounds per barrel. The Lot-O-Tumbler holds about 4.5 pounds of rocks.

Selecting Rocks

There are many sites that educate on the types of rocks and hardnesses. I select hard rocks with a Moh’s hardness around 7-9. I have a multi-tool that has a steel file. If the file scratches the rock, then the rock is probably too soft. I also look for rocks that have a “waxiness” look to them. Agates are always good, along with Jaspers, and any Chalcedony type of rocks.

Stage 1

I use my rotary tumbler exclusively for Stage 1.

• Fill the barrels about 2/3 to ¾ full of rocks.
• Add water so it comes up BELOW the top layer of rocks.
• Add 3 tablespoons of 60/90 silicon carbide grit
• Close the barrels according to the manufacture’s method
• Tumble for 1 week.

At the end of 7 days tumbling, I rinse the rocks well. (DO NOT POUR DOWN YOUR DRAINS!!!) I go through each rock and examine them. I put them into two categories – 1) Smooth enough to go onto the next stage, 2) Not smooth enough.

I take the NOT smooth enough ones and place them back in the barrels. Add more rock to bring them up to the proper lever as described above and set them up as above and run them for another 7 days.

I repeat this process until I have enough rocks to go on to the next stage. Sometimes, certain rocks will tumble for several weeks, or more than a month before I decide to let it go on to the next stage. It is totally up to you how “picky” you want to be and how smooth you want your rocks. Some people will tumble them until there are no more cracks or chips showing anywhere. I don’t have the patience for that, so my “pickiness” is somewhere in between.

Stage 2

When I have enough “smooth enough” rocks from stage 1, from the rotary tumbler, I send them to Stage 2 in the Lot-O-Tumbler, vibratory tumbler. The rest of the stages are done in the Lot-O-Tumbler.

• Fill the Lot-O-Tumbler barrel to about the widest spot in the barrel.
• Fill barrel with water above the level of the rocks.
• Hold hand over top of barrel and tip barrel upside down. Let the water drain out of the barrel so the rocks are wet, but there is no standing water in the barrel.
• Place the barrel in the Lot-O frame.
• Add 2 tablespoons of 120/220 silicon carbide grit
• Put cap on barrel
• Turn on tumbler.

You can take off the cap and look at the rocks. They should be rotating in the barrel. I let them run for about 12 hours. After 12 hours, I add small and large ceramic media to make the barrel close to full. I have been having trouble if I add the ceramic media at the start of the stage, many times the all of the grit will end up on the bottom of the barrel with most of the ceramic media. I’ve found that if I wait until the silicon carbide starts to wear down a bit, then add the ceramic media, I have better results. Once the ceramic media is added, I let the tumbler run for a TOTAL of 2 days (1 ½ days since adding the media). Check it a couple times of days and add water as needed. I use a squirt bottle and add 10 or 15 squirts. If the grit is too dry, it is very difficult to clean out of the cracks of the rocks. If the grit is too wet, it won’t stick to the rocks and end up on the bottom of the barrel. Experience will teach you the proper amount.

After 2 days add a squirt of Dawn liquid dish-washing soap. Also add a little water, just enough until the tumbling action begins to slow down. Not too much. Let it run for 15 minutes.

• Rinse and wash the rocks thoroughly. Wash out the barrel very well also.
• Place all of the rocks and ceramic media back into the tumbler.
• Fill with water.
• Hold your hand over the top and drain the water out until the rocks are wet but no standing water in the tumbler.
• Place the barrel in the tumbler frame. Turn on.
• Add a squirt of Dawn soap and a little bit more water until the tumbling action just starts to slow a bit. Put the lid on and let it run for 45 minutes.

With the tumbler still on, after 45 minutes, fill the barrel completely full of water. Put the lid on, and let it run for 15 more minutes.

Rinse and wash the rocks thoroughly. Wash out the barrel very well also. On to stage 3. Do NOT dry the rocks between each stage.

Stage 3

• Place the clean rocks and media from stage 2 back into the clean barrel.
• Fill with water
• Put hand over opening, turn barrel upside down and drain water. The rocks and media should be wet with no standing water in the barrel.
• Put barrel in Lot-O frame and turn on.
• Add 1 tablespoon of Borax.
• Add ½ teaspoon of 500 grit Aluminum Oxide grit.
• Tumble for 3 days.

Examine the rocks and add water as needed. You want a consistent creamy film around the rocks. I look at the rocks a couple times a day (morning and evening) and give them 10 squirts or so of water as needed.

• After 3 days, add a squirt of Dawn soap and a bit more water as before. Let it run for 15 minutes.
• Rinse thoroughly as before.
• Place rocks and media back in the clean barrel.
• Fill with water and drain as before.
• Place on Lot-O frame and turn on.
• Put a squirt of Dawn in barrel and some water as before.
• Let it run 45 minutes.
• Fill completely with water and run additional 15 minutes.
• Rinse thoroughly as before. Make sure the barrel is very clean.

Stage 4

• Place the rocks and media from stage 3 back into the clean barrel.
• Fill with water
• Put hand over opening, turn barrel upside down and drain water. The rocks and media should be wet with no standing water in the barrel.
• Put barrel in Lot-O frame and turn on.
• Add 1 tablespoon of Borax.
• Add ½ teaspoon of Aluminum Oxide Polish.
• Tumble for 2 days.

Examine the rocks and add water as needed. You want a consistent creamy film around the rocks. I look at the rocks a couple times a day (morning and evening) and give them 10 squirts or so of water as needed.

• After 2 days, add a squirt of Dawn soap and a bit more water as before. Let it run for 15 minutes.
• Rinse thoroughly as before.
• Place rocks and media back in barrel.
• Fill with water and drain as before.
• Place on Lot-O frame and turn on.
• Put a squirt of Dawn in barrel and some water as before.
• Let it run 45 minutes.
• Fill completely with water and run additional 15 minutes.
• Rinse thoroughly as before. Do not dry the rocks before doing the next step.

Final Process

I have very hard water. Sometimes, when the rocks are done, they will have a slight film on them and any cracks would really show up as they dry. I now do the following, which greatly improved the outcome.

• After the rocks are completely done, and still wet, put them in a microwave proof container. I use a plastic 8 cup measuring container.
• Fill the container with DISTILLED WATER so the rocks are completely submerged.
• Add a small squirt of Jet Dry (Rinse agent for automatic dishwashers) and mix it all together.
• Put the filled container in the microwave oven and warm it all up. 1 or 2 minutes. Make it nice and warm, but not so hot you can’t handle it. (Someone warned me about putting rocks in the microwave oven, but the rocks are completely submerged and only warmed up)
• Pour the water out and collect the rocks. Place them on a paper towel to air dry. Do NOT rinse them again with tap water.

All done! Sort and enjoy your polished rocks.

You can download this post as a pdf file using this link:
Our-Procedure-for-tumbling-and-polishing-rocks.pdf