Black coral is almost woodlike. It is fibrous and has growth
rings like a tree. It's not that rare. It grows in the channels
off the Hawaiian Islands, around the Phillipines and Indonesia
and probably other Pacific Islands. The stuff around Hawaii is
in deep water, 100+ feet and takes skilled diving to harvest.
It has to be dried for months before it can be cut. We wait a
minimum of 6 months.
The thin branches can be soaked and bent. You can bandsaw the
coral and cut cabochons quite easily. You can shape it with
files (dulls them), grinding wheels, belt sanders, diamond
burs, saws, assorted steel burs, sanding discs, etc. You can
progressively sand and then polish or you can hit it with
bobbing compound if you like. It polishes to a shiny surface
with yellow rouge.( Note: You can burn the coral if you let too
much friction build up. The burnt coral behaves like burnt
wood. It discolors and doesn't polish well.)
Depending on the way the coral grew, you can have different
densities, knotholes, gaps between the growth rings, imbedded
shells, etc. Sometimes, you can not achieve a fine polish
because the coral "orange peels" or has a coarse grain. Also,
the outer "skin" is rough to the touch like sharkskin so you
would want to remove the outer skin before doing any bending
and forming of branches into bracelets.
The coral is absorbent so you don't want to soak it or expose
it to chemicals and perfumes. Like polished wood, it scuffs and
scratches. It can shrink even after prolonged drying/curing if
exposed to hot lights.
In Hawaii, the harvesting is regulated. Stumps have to be a
certain diameter and you can't dredge for coral. You have to
dive and selectively harvest. The same can't be said for other
parts of the world.