Moonstone is an incredible rock, shimmering with an inner beauty that few can match. Of course, that’s when it’s been properly cleaned, cut, and polished. Raw specimens can be impressive, but they’re not quite what most of us are going for. Instead, you’ll want to clean and polish your specimens.
So, let’s get to it and I’ll explain how to clean and polish raw moonstone!
What You Need
I’m going to describe a simple process that can easily be done with just hand tools or a Dremel rather than one using specialized equipment.
For tumbling see our guide to tumbling rocks. Moonstone is a feldspar mineral and is safe to tumble with others in the group like labradorite or sunstone. Minerals of this class range from 5.5 to 6.0 depending on the individual stone, so choose accompanying rocks accordingly.
For cutting cabochons, you’ll want to take a look at our guide to cutting cabochons after slabbing the stone.
For an individual specimen, hand detailing is often the way to go. If you follow through with this process you can also make a carving out of moonstone during the rough shaping process if you’d like.
You’re going to need the following items for this task:
- Rotary Tool– Ideal, but optional. A basic grinding kit will get you all of what you need for a specimen or simple carving. A flex shaft attachment is ideal if you aren’t using something like a Foredom.
- Sandpaper– 400 to 2000 grit is fine, I prefer to go to 3000 with feldspar minerals before polishing. You’ll want 80-120 if you’re going to try shaping with sandpaper.
- Lapidary Files– If you don’t have a rotary tool, pick up a set of flat lapidary files. They’re not the fastest tool to use, but they’ll cut much quicker than sandpaper when it comes to rough shaping.
- Cerium Oxide– For the final polish, cerium oxide is an ideal material.
Zamwill also work, but in this case, I prefer to use it after cerium oxide as a sort of “super polish.”
- Dawn Dish Soap- For the initial cleaning. Any dish detergent should work, but I know Dawn does so it’s what I’ve consistently used for over a decade.
- A Bucket, Pot, or Cooler- To contain water while you’re working and keep the piece wet.
These basic tools and materials will help you get a great polish after cutting the stone to shape. This method will also work for slabs of material if you have them. Slabbed material is great for those with few tools since a Dremel with the right cutting discs can be used as an improvised trim saw.
You’ll also need PPE:
- Safety Goggles/Glasses- Goggles are preferable due to the high probability of water containing grit hitting your face. Glasses will work fine if they’re all you have, but grab a rag to wipe the mud off your face if that’s the case.
- N95 Mask- Moonstone is relatively benign as far as stone dust goes… which just means it takes cumulative exposure to kill you instead of causing an acute reaction. Use a dust mask, and upgrade to a respirator if you’re working in an enclosed workshop that doesn’t have a good ventilation system.
With your things gathered together, you’ll be good to go as long as you have time. Expect to spend at least an hour or so per 1-2” stone, but this will speed up with experience.
Step 1: Clean Thoroughly With Soapy Water
Fill up your bucket, drop in a squirt of Dawn, and go to town with an old toothbrush or a nylon brush for a few minutes.
Dawn will take care of surface dust and debris, as well as the oil that stones are sometimes shipped in. This oil is used to create a more “whole” appearance in cracked stones, but it also lets them slide past each other in the parcel. This is acceptable with rough material, but I’d find a new dealer if they’re shipping you cut stones that way.
Pull the stones after a good brushing and examine them.
You may have some dirt and other junk jammed into crevices. Ignore it for now, it’ll come loose when you cut that portion of the surface away.
Let the stones dry afterward. No need for any extreme measures this time around, a good washing will do it.
Don’t dump the water in your sink, toilet, or bathtub. Instead, go dump it outside. The rock dust is inert and won’t damage anything outside but it can build up in pipes and create a blockage that’s immune to the normal chemical methods of clearing a drain.
Step 2: Examine Stones Carefully
Get a good look at your stones before you dig in.
In my experience, “regular” moonstone tends to be pretty solid, but it’s important to identify any large fractures on the exterior of the stone. Rainbow moonstone (which is just clear labradorite) tends to have more fractures depending on the grade of the rough.
You’ll also want to figure out which faces need the most work and how you’ll go about shaping the stone in the next step.
Areas with heavy fractures can be filled with stabilizing epoxy, ground off, and in some cases broken off. You won’t always be able to get rid of everything, but it’ll pay to know which bits are going to crumble when you’re working on them.
There’s more to this than fractures, however. Most of us want to get the optical effect that moonstone is known for, which requires some attention to angles. It’s a similar process to cutting labradorite for effect.
Step 3: Rough Shaping
Get your bucket, cooler, or another container ready, and find a comfortable place to work. If you’re using a rotary tool you should be careful of the backdrop, especially if you don’t know the splash pattern yet, but anywhere is usually fine.
It’s not uncommon for me to watch TV and have a bucket at my feet if I’m using hand tools, for instance.
You’ll now want to smooth and round the faces of the stone. Use a diamond grinding wheel or a rough, flat, diamond file to grind down any protrusions and even out surfaces.
Keep the stone wet at all times. You can observe the mud created while working to know when it’s a good time to dip the stone. Once it goes from transparent to milky white and starts to thicken you should dip the stone again.
With a flex shaft you can actually work in the water, but don’t stick a normal Dremel directly in or you’ll be in for a shocking surprise.
Puns aside, don’t stick power tools in water. Flex shafts are an exception since they only contain mechanical pieces and won’t transfer water up to the motor of the tool.
Work the stone’s surface until you’re happy with what you see.
Step 4: Sanding
Sanding is easy but time-consuming and requires attention to detail. I much prefer to hand sand when I’m working without a cab machine, but you can use a basic sanding kit and your rotary tool as well.
Sanding is just a matter of progressing through the grits. This is still a wet process, so keep an eye on the stone even if you’re hand sanding.
For feldspar family minerals I’ll usually start with 400 and work my way through 2000 or 2500 before polishing. I just go with the next grade of paper I have, since I usually purchase packs of quarter strips.
After each step in the sanding process, you should stop, dry the stone entirely, and examine the surface. You want a uniform surface with no deeper scratches, otherwise, you need to continue with the grit you’re using.
After 800 grit the stone will begin to get shiny, rather than having a matte surface.
I find it pointless to go much beyond 2000 with feldspar minerals, but I’ll sometimes go up to 3000 out of habit or for exceptionally dense pieces.
As long as the stony is shiny, you can begin to polish. That said, higher grits will provide a better surface once polishing is done.
Step 5: Polishing
With our stone cleaned, shaped, and sanded… well, we’re ready to begin polishing!
There are a few ways to polish the stone using the cerium oxide I described above:
- Buffing Machine/Bench Grinder- Felt is better than cloth for cerium oxide, but you can use whichever wheel you have on hand. 3-inch models are great for places with limited workspace but you’ll usually need to order the polishing wheels online.
- Felt Wheel on the Rotary Tool/Flexshaft- Felt wheels are plentiful and easy to find. If you’ve ever bought a kit for your Dremel you probably have a few, otherwise, just grab a couple wherever you can find them. A cheap kit will last for a long time.
- Hand Polishing- Using a buffing rag or piece of leather you can also hand polish. This is time-consuming but it still yields a great finish as long as you’ve sanded correctly.
Check the stone before you begin polishing and make sure that there aren’t any scratches that you can’t live with.
Regardless of what you’re doing, mask up when you’re polishing. The array of cloth, polishing compounds, and stone dust in the air is a nasty combination.
Make a paste with cerium oxide and a little bit of water. I prefer distilled water to avoid calcium stains when finished, but the tap will work fine. The paste should be thick enough to hold together well, but not runny.
Charge the wheel or cloth you’re using. For a buffing machine press the paste gently into the wheel, a rotary or polishing cloth can pick it up from wherever you mixed it in the first place.
With a buffing machine, you can just hit the stone all around until you’re satisfied. It’s easy, but the stone will heat up quickly without a bit of water added to the process.
With the other options, just move the polishing wheel or cloth in small circles, about the size of a dime, and continually work over the surface of the stone.
When satisfied, you can either call it good or hit the stone with a second polish for a “super polish” effect. This is usually just a lot of work for very little gain, but many swear by using tripoli or
Super polish or not, you’re now done and it’s time for the most important part: being able to sit back and admire your craftsmanship.