Because of its glass-like, cryptocrystalline structure, obsidian can be a challenge to polish. Attempting to polish the stone in a tumbler can easily result in seriously fractured pieces, no matter what precautions you may take. As a result, many collectors opt to polish obsidian pieces by hand to ensure they remain whole and undamaged.
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How To Polish Obsidian By Hand
There are a number of hand-polishing options to be found on the internet. Forum sites argue the efficacy of various polishing mediums and cloths. But most of them agree that cerium oxide is the preferred polishing agent for obsidian. Beyond that, prior experience and personal preference reign.
Some collectors choose to polish just one side of a rough obsidian stone for the sake of showing the contrast. And to be honest, this is what I really prefer. Another benefit to polishing obsidian this way is that it drastically shortens the time and effort required to get the desired result. The choice to do it this way may depend on how rough your stone is to begin with. And a simple buff may not be enough to produce the shine you’re going for on a rough stone.
Using a Polishing Cloth
Damp wool felt with a light coating of medium can be depended on to produce a high shine on smooth stone. Make sure neither the medium nor cloth is over or under wet. This will help minimize the possibility of scratching without allowing the polishing medium to cake and become difficult to manage.
There are also those who swear by leather instead of felt. The leather will need to stay moist and be combined with a thick slurry of polish for the best results. You’ll need to rub fairly hard in a circular motion, and stop before the leather dries out. Dampen the leather and go again, repeating until you’ve achieved the maximum shine.
Polisishing Obsidian With a Lapidary Wheel
If you’re careful and experienced, it is possible to polish obsidian with a lapidary wheel. A 12-inch wheel covered with 1/2-inch thick office-style carpet can be ideal. The wheel rotation should be fairly slow, around 400 rpm. Dampen the carpet and polish with cerium oxide for about 5 minutes at a time before stopping to re-dampen. Use a spray bottle with water plus a few drops of dishwashing detergent to wet the carpet.
Basic Hand Polishing Instructions
Basic hand polishing of stones involves moving from a heavier grit to a finer grit sandpaper to remove rough edges and imperfections. But when hand polishing obsidian, it’s recommended that you not use too heavy a grit sandpaper, or you risk damaging your stone with deep scratches that will be difficult to remove.
Here are the basic steps for hand polishing obsidian. The process can take many hours of patient labor. You may need to proceed in stages to achieve your goal. For this basic polishing procedure, you will need:
- Obsidian stone of choice, a fairly smooth piece is preferable
- An ample supply of 600, 1200, and 3000 grit sandpaper
- Cerium oxide polish
- Wool felt or a lapidary polishing cloth
1. Cut fairly fine grit sandpaper into small pieces, 1-2 inch square. You can expect each piece to last around 5 minutes or so, so cut plenty. Recommended grits are 600 and 1200, with 3000 for the final buff. If your stone is fairly rough, you may want to add a lower grit paper to start with.
Instead of cutting the sandpaper, you may opt to rub your stone against a whole piece resting on a stable, flat surface. The results should be the same. Move the stone continually on the sandpaper to ensure all sides are sanded evenly. Using the small pieces may be advantageous if your piece has many dips or curves.
2. Begin sanding the rough edges first with 600 grit paper. Continue buffing until there seems to be no further improvement. This stage generally takes several hours to complete.
3. Repeat the process with the 1200 (or next finer) grit sandpaper to remove smaller imperfections and scratches in the surface. Use a circular motion to minimize the possibility of making marks on the surface. The stone should begin to reflect with a light shine by the end of this step, and there should be no visible scratches.
4. With cerium oxide and your cloth of choice, buff the stone to the desired shine.
You may also consider a final buff with a .2 micron polishing compound. Though the entire polishing process takes time and patience, the results will be a piece worth bragging about.