Hello all you people out there in jewelry land! Does anyone know
how to polish red branch coral?
I also clean these stones in the ultrasonic cleaner and steam. If left in the
cleaner too long, they will come out dull.
This comment and a couple of others could possibly be taken to
indicate it’s the ultrasonic sound waves that dull the finishes
of coral and malachite. Both materials are carbonates and the
finishes are damaged by acids that may be present in the
ultrasonic cleaning solution, not the ultrasonic waves (although
they are soft and could be damaged by abrasion with the metal of
the tank) . The reaction is similar to pouring vinegar onto
baking soda. Unless you want a repolishing job, keep these
materials away from all acids; also rhodochrosite, azurite and a
few others. Since lots of drusy minerals are now being used in
jewelry, be very sure you know what the minerals are before
dunking them into any acidic solution.