Should I Use Oxide Polish or Diamond for Polishing Gems?
What's the best abrasive for polishing natural gems? An oxide polish is usually the best option. Learn the different uses of oxide and diamond polishes.
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Recommended Polishes For Natural Gemstones
I cut natural gemstones almost exclusively. The majority, with the notable exception of sapphire and chrysoberyl, are easily polished with an oxide polish, either aluminum oxide(Al2O3) or cerium oxide (CeO2). Diamond polish tends to work best on hard stones, hardness 8 and above. On softer stones below hardness 8, diamonds are much more problematic.
Stones Typically Polished With Cerium Oxide
I rarely cut the following, but these should also be polished with cerium oxide.
Stones Typically Polished With Aluminum Oxide
Garnet of all types (almandine, demantoid, spessartite, pyrope, grossular, uvarovite), peridot, tanzanite, tourmaline of all types (achroite, dravite, elbaite, indicolite, rubellite, schorl, siberite, verdelite), spinel, zircon.
I rarely cut the following, but they should also be polished with aluminum oxide.
Stones Typically Polished With Diamond
There are some exceptions, depending on the individual stone. In some cases, as stones get larger they may require diamond instead of an oxide polish. Some stone types I occasionally polish with diamond are topaz, zircon, and spinel. Sometimes I use diamond on a problem stone or even a problem facet.
Using Oxide Polish
I prefer to use an oxide polish on almost all my gemstones. I know some experienced cutters prefer to use diamond on various laps (such as ceramic, tin, or copper). To each their own. You can polish in many different ways. Go ahead and try different polishes and laps. However, I've found there are various reasons oxide polish works better than diamond polish on most natural stones. I think inexperienced cutters can benefit from this knowledge.
Oxide Polish Works Faster Than Diamond Polish
It's been my observation that oxides work faster. Generally, aluminum and cerium oxides leave higher quality finishes than diamond. Many oxide polishes are 0.3 micron or finer, depending on the manufacturer, which is close to 100,000 grit.
A typical diamond polish scenario would be to cut the stone to 1,200 grit and then switch to diamond pre-polish and polish. Generally, the steps would be something like this: 3,000 (for a large stone), 8,000, 14,000 (not always used), and 50,000. Some people may polish to 100,000 diamond, but most don't go finer than 50,000 on an average diamond polish.
A typical oxide polish scenario (for me) is to cut the stone to a worn 1,200 grit lap and then polish with either cerium or aluminum oxide. That's it. Done.
Oxides are one step. A diamond polish is a minimum of two steps, and many stones require 3-4 extra diamond polish stages. Remember, on every step/polish you'll have to cut/polish every facet on the entire stone. Let's say you're dealing with a gemstone that has 100 facets. Depending on the stone and the extra polishing stages you need to set up for a diamond polish, you could be looking at polishing the equivalent of 500 to 600 facets!
Think of the hours that four extra diamond polish stages will take.
If your gemstone can be polished with oxides, that's a better option. Every pro I know, including myself, uses oxide polish extensively. That should tell you something.
Polishes for Contest Cutting
Of course, I'm not talking about contest gem cutting conditions, where a slow diamond polish is easier to control for meets under high power. However, I would note that many competitors "kiss" contest stones with oxide polish after the diamond polish to give them a final "pop."
Lap And Polish Combinations
Spectra Ultra Laps
For beginners or those who don't cut many stones, Spectra Ultra Laps are a good, inexpensive choice. You can charge them with whatever oxide polish you need, and they'll work well. If used properly, they will actually polish nice, flat facets. A light tough and a good pre-polish are the secrets that prevent rounding.
(I know several guild contest winners that use Ultra Laps to pop their stones before sending them to the judges. Some won't admit it because they don't want people to know what they're doing).
I probably use a tin lap with aluminum oxide the most, mainly because I tend to cut a lot of garnet and tourmaline.
Since zinc laps are no longer readily available, I generally use tin laps with diamond polish when necessary. (I use one 8,000 and another 50,000 diamond charged tin lap).
I'm finding that I like phenolic laps and use them often. They work very well with any oxide polish and are very inexpensive, too. I don't recommend these for beginners. They can be a little fussy when lining up a facet to be polished. I do recommend phenolic laps for advanced cutters. In most cases, these laps aren't quite as fast or easy to use as a good tin lap, but I've found they help solve some occasional polishing problems. In some cases, they polish as fast and sometimes better than a tin lap.
Oxide Polish is Easy to Use
I want to point out one last thing. Have you ever noticed all the people on online forums talking about troubles with their charged diamond polishing laps? Notice how often they talk about how to clean them, get them to stop scratching, recharge them, resurface them, or fix them in general.
Have you ever noticed anyone discussing these troubles with an oxide polish lap? That should tell you something.
Your polish and lap choices depend on the gem material you're polishing. If you're dealing mostly with natural gemstones and not using oxide polish, you're missing out on a faster and easier way to get the job done. Personally, I couldn't do without my aluminum and cerium oxide polishes.
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