Lapidary
Tips – Cabochon Polishing Tip by Dick Peterson,
TG&MS
About 15 or 20 years ago, when I was
cutting a lot of Bertrandite, I ran into a problem I hadn’t seen before. I had
been shaping and sanding and polishing a lot of cabs when I had one that
wouldn’t polish. The stone was a deep dark purple, one that I though would be
outstanding. I went back to my Genie and re-sanded it and tried polishing it
again. No luck. I set the cab aside and forgot about it.
 |
| Snowflake Obsidian 25mm Cabochon |
One
day I was using some acetone and I spotted the cab so I cleaned it in the
acetone. I then washed it in Dawn® Soap and warm water. Then I tried it again
on the polishing wheel…it took a beautiful polish! What had happened during the
cutting stage? It had been cut with oil and it had absorbed some oil. Oil is
not a friend in cutting and polishing cabochons.
If you suspect that
the rock you are about to cut will absorb oil (some softer rocks do this) try
the following before you cut it. Soak the rock in water for 24 hours or longer
(longer is better). In the summertime put the container of the soft rock in the
sun where it can warm up (the warmer the better). Keeping it warm helps the
rock absorb more water. Next put the rock in the slab saw and cut it as soon as
possible. The oil will slowly replace the water in the rock. Now is a good time
to wash the slab with acetone. Anytime you cut slabs in your slab saw you
should always place your slab in kitty litter (which is a great way to suck out
the unwanted oil), wash your slab in warm soapy water. Dawn dish soap is one of
the best to use.
By Dick Peterson; Timpanogos Gem & Mineral
Society, Provo, UT
Rock Chips, December 2011
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