Which Is The Best Polishing Compound To Use For Rocks?
Polishing compounds are a hot topic among lapidaries, with opinions clashing constantly. There’s a good reason: the difference in the final polishing of a stone can make a huge difference in the final look. So what is the best polishing compound for rocks?
It depends. Sit down and dig in, I’m going to break down common polishes, how to choose, and give you some tips to help you get the best possible polish.
Learn everything you need to know to polish rocks with a rotary tool!
Weighing Your Options
There are a lot of options available for the prospective lapidary, which means choosing the right one is a priority.
Keep in mind we’re only talking about these compounds as a final polish, none will show enough abrasive power to even out nicks, scratches, or pitting. Those problems should be handled before you reach the polishing stage.
For rocks, there are various oxides and extremely high grit diamond paste available.
Proprietary Blend of Ingredients
The problem is that each polish is its own proprietary blend of binders, abrasives, and waxes. Quality control is what separates good polishes from great ones. It’s why you’ll find Zam in the workshop of the majority of silversmith’s workshops: it’s formulated well, it does what it’s supposed to, and every block or tube of the stuff will work exactly the same.
Unfortunately, a lot of the information that we’d normally use to make decisions isn’t available with polishes. While it would be handy to have things like micron size or abrasive composition on hand, companies aren’t under any obligation to share them with us.
And, of course, everyone has their own way of doing things when it comes to getting a great final polish.
Method of Polishing
Then we run into how you’re polishing your rocks. Doing things with a flex shaft and doing them in a tumbler are very different. You also have flat laps and polishing wheels to consider, depending on the tools you have access to.
Things To Look For
But here are the important things to evaluate when looking at polishes:
- Reputation- A good reputation is important, even when abrasives are the same compound there is differing quality. It’s best to stick with brands that are well known if you’re using a complete polish and not a powder.
- Compound- Which compound works best depends on the stones you’re working with. Many commercial polishes are also a mix.
- Form- Waxes are easy to use right out of the tube, while powders require a little bit more prep. On the other hand, powders are your only option for tumblers, so you’ll need to choose the right compound for your use.
- Grit- Some polishes will reveal their grit size. This is important, as smaller grits will work to create a smoother final polish but have less abrasive action to fix any problems that showed up during shaping and sanding.
Keep this in mind when you’re looking at polishes. If you’re not sure of the exact compound in a polish you can usually do a quick search to find out at least the constituents. Don’t expect an exact breakdown of ingredients, however, since commercial polishes are “secret” blends in most cases.
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Choosing the Right Compound for Your Stone
Your rock and the method you’re using to polish them will pick your polish for you.
Every rock is different, but so is every lapidary. While I’ll be supplying general guidelines for choosing a polish, there are always disagreements and I’ve seen how in-depth some rockhounds go for getting the best finish on their stones.
As a general rule, the hardness of the stone you’re working with is the best guideline as to what the primary polishing ingredient should be.
Everyone has their own system. And it probably works, at least if they’ve been at it for a while and modifying their techniques and compounds to get the results they want.
These range from complex arrangements of specific grits separated into polishing, buffing, and “super polishing” to much simpler systems.
Silicon carbide, a favorite for lapidary wheels, is not a suitable polishing compound in most cases.
If you’re willing to experiment, I recommend the following as a good place to start:
- Soft Stones (3.0-4.5)- Zam
- Hard Stones (5.0-7.5)– Cerium oxide
- Very Hard Stones (>8.0)- High grit diamond paste
For most tumbling applications, the usual aluminum oxide grits will do just fine.
Diamond paste is a pain to use. It cuts slower than oxides and generally requires more stages. Two stages are the minimum, most of the time you’ll see three to five. That said, it’s a great compound when you’re working with flat laps and careful application will give you an incredible polish.
So, What’s the Polishing Compound for My Rocks?
If I was pressed to recommend a single polish to a prospective lapidary without knowing what they’re cutting I recommend cerium oxide.
It’s a bit harder to use than most premixed polishes, but it will handle the final polishing of everything from fluorite to quartz without any problems. It can also be used to polish things up to the hardness of beryl (ie: emerald, heliodor) without a problem.
Unfortunately, diamond paste stages will be required for anything much over an 8 on Moh’s scale. The only commonly used lapidary material in that range is corundum derivatives, so you’ll know when you need to upgrade.
I do have one further recommendation: Zam is specifically designed for turquoise and works well for all softer stones including opal. If you work with silver or copper it’s also an incredible polish for nonferrous metals.
One of those three will get you a very nice polish on your stones. That said, I always advise talking to people who work in the same material. Many lapidaries have come up with intensive routines for their favorite stones, and learning from the experience of others is valuable.
In the end, the best polish is the one that works. With that said, the above guidelines should help you choose a polish that’s suitable for the stones you’re planning to polish!
If you’re looking for more specific information on individual polishes, why not check out our guide?
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