Rock polish is the media used in your tumbler to grind down the rough edges and eventually polish the surface of stones. Sometimes it refers to just the final polish but can also be more broadly used to include both finishing polish and the coarser grits used earlier in the process. Let’s go over all the types of grinding and rock polish so you will understand the entire rock polishing process.
4 Step Tumbling Process
Commonly, a 4-step process is used to polish rocks. The first 3 steps start with a coarse, silicon carbide grit and move on to progressively finer grits of silicon carbide with a final polishing step 4 using a polishing compound like aluminum oxide.
Why use Silicon Carbide
Silicon carbide is a very hard compound with a hardness of 9 on the Mohs hardness scale. This is generally harder than the rocks being tumbled which means the grit won’t wear down.
Although the first 3 stages all use silicon carbide, the particle size varies. The earlier stages utilize a larger grit size (coarser) for more abrasion while the latter stages use a small grit size (finer) to begin to polish instead of abrading.
Step 1 Coarse Grit Stage
Step 1 is used to round all the rough edges of your stone mix. Our first stage grit is 60/90, meaning the grit particle size is a mix of anything from 60-90 grit size. The smaller the number on the grit scale denotes a larger size particle. Since the first step is coarse removal of material, any particle around this size should work. Some people prefer a specific size but 60/90 is accepted as a good first step grit size to use. This stage will produce the most sediment with the largest amount of rock ground away with the coarser grit.
Step 2 Medium Grit Stage
Step 2 does further shaping and begins smoothing the faces of the stone. Our silicon carbide for this step is 180/220 grit. As with 60/90, 180/220 can contain a mixture of sizes anywhere from 180-220 grit size. Also mentioned before, these numbers are larger than 60/90 grit so 180/220 grit has smaller particle sizes, meaning finer particles.
Step 3 Fine Grit Stage
Step 3 uses 500 grit silicon carbide to smooth the faces. Your rocks should be very smooth after this stage, but they may lack polish and shine.
Types of Polishing Compounds
Step 4 and latter polishing stages (if desired) will use polishing compounds. Some types include:
- Aluminum oxide
- Tin oxide
- Chrome oxide
- Cerium oxide
Aluminum oxide is the most common rock polish used and the one we sell for our Stage 4 polish. There are different types of aluminum oxide so it is important to choose a premium brand. We use a proprietary aluminum oxide, proper micron size and with enough surface area to do a good job of polishing. Aluminum oxide is a cost-effective way to get great results.
Tin Oxide, Chrome Oxide, Cerium Oxide
These polishes are more expensive and not used by most people. Tin oxide produces better results for softer stones, and cerium oxide provides better results for glass and obsidian. Chrome oxide is mainly used for harder stones like jade and nephrite.
Step 4 Rock Polish Stage
As mentioned, Step 4 is the final polishing step. It is the most critical step since it is very frustrating to go through a 4-week tumbling step and not have your stones nicely polished when it is done.
The 4-step process should be adequate to produce a good result. But some people will do another step after step 4 to try to get an even nicer finish. They will usually use some of the more expensive oxides like cerium oxide.
Also, some might slip in an additional step somewhere in the earlier stages too. For instance, they may use an 800 or 1000 grit silicon carbide between steps 3 and 4.
Other Post-Polish Steps
If you are unhappy with the amount of gloss you get after completing the 4 steps, you can burnish the stones with soapy water. Cut some shavings from a bar of Ivory soap and put in with your rocks and cover with water. After a few hours, the soapy mix will coat your stones and make them glossier.
Amount of Grit and Polish to Use
We recommend 2 TBS. of grit for Steps 1 and 2, 1 TBS. for Step 3 and 1.5 TBS. for Step 4 polish. Many people think that more grit will do a better job and end up using too much. You will see all kinds of recommendations for how much to use but we have had great results using the amounts above. As people tumble more and gain more experience, they develop their own preferences on how much they like to use. They will also modify based on what rocks they are tumbling.
Use of Fillers
Many people also use fillers along with the grit. Tumbler filler media is useful for several reasons: filling in the empty spaces of your tumbler, cushioning stones from bruising and breaking, improving tumbling action and reducing noise.
It is recommended to fill your tumbler to 2/3 to ¾ full with material. If your rocks don’t fill this area, tumbling media is a good way to make up the difference.
You can use either ceramic media or plastic pellet media, as filler.
Our ceramic tumbling media is in the form of ceramic cylinders, with angle cut sides. This shape is good at transporting grit to hard to reach places. Ceramic tumbling media should be non-abrasive, so it doesn’t abrade the rocks, that is what the grit is used for. We sell large, small and mixed size cylinders. Each has its purpose and people develop their preferences as they gain experience tumbling. Large ceramic is used to fill large voids in your tumbler. Small ceramic is good to get into hard-to-reach places in the rocks and rock mixture. Finally, a 50/50 mixture by weight is a good balance of the two benefits. Ceramic can be used in both rotary and vibratory tumblers.
Our poly plastic tumbling beads are high-impact polypropylene that is designed to handle the harsh environment inside the tumbler barrel. Plastic has been used for years and is still preferred by many people although people like ceramic since it is easy to wash and re-use. Plastic pellets can be re-used but only in the same step in which they were previously used, since that stage grit becomes embedded in the plastic pellet.
How long to tumble each step?
Our instructions recommend running each tumbling step for 7 days. This is a good round number and seems to work, in general. But it is always best to check after a few days, just to make sure. This is particularly important in Step 1. If you are newer to tumbling or tumbling a new type of rock, you may find that the stones are of the softer variety and running them too long in coarse grind will wear away more rock than you like. So, check just to make sure.
As you gain experience in tumbling, you can develop your own preferences as to how long you want to tumble at each step and vary from the usual 7-day rule.
Tips to Achieve Best Performance
- Separate your rocks by hardness and then only tumble rocks together with like hardness. This will prevent harder rocks from marring softer rocks during the polishing stages.
- Don’t reuse grit. Dispose of it outside. Don’t pour into any sinks, toilets, sinks, etc. It will act like cement in your drain pipes once it dries out.
- Do a thorough job of washing off your stones and rinsing out your barrel before moving to the next stage.
- You may have to re-tumble some stones in the early stages in order to remove pits. Just tumble the stones that need more work – if some have been tumbled enough, you can separate them out.
Other FAQs about rock polish
Can I use Polly Plastics grit and filler with any tumbler?
Yes, our tumbling media can be used with any brand tumbler.
Can I use Polly Plastics tumbling media with any type of rock?
Yes, you can use our grit and fillers with any type of rock. And we include easy-to-follow instructions with our kits.
We sell 2-packs of each step, i.e., 2 packs of Step 1, Step 2, Step 3 and Step 4. We also sell the grit in 4 step kits. We sell 3 kits: a grit only kit, a grit kit with plastic filler and a grit kit with ceramic filler. We also sell filler on its own, i.e. single and 2 packs of small, large or mixed size (1/2 small and ½ large, by weight) ceramic and plastic pellet filler in 1 and 2 lb. packs.