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Tumbling emeralds


I am new to finishing stones and am going to try and tumble about a
pound of rough Brazilian emeralds mostly still in their black
matrix. I have a couple of questions. Can I use small agates with
the emeralds to make up remaining stones to fill the tumbler? and
whats grits I should use?

Thank you in advance for your help, I can’t wait to get started!!


Can I use small agates with the emeralds to make up remaining
stones to fill the tumbler? 

The basic rule for tumbling is to use like hardness material, and
like sized material. IE don’t try tumbling some obsidian with some
topaz. The topaz will eat the obsidian. Like wise, don’t try to
tumble 1/4" stones with 2" ones as the larger will do a number on
the smaller ones.

As to grit, tumbling is usually a four step process, sometimes five.
Start with a course grit, go to a fine grit, follow with a pre
polish and then polish. Some times, a burnishing step will put the
final kiss on the stones. You will have to judge the length of time
in each step by the results you get. Some serious tumblers set
aside a couple stones from each stage for comparison to the stage
they are working.

A problems with tumbling stones like emeralds still in matrix, is
that the matrix is not the same hardness as the emeralds, and so the
exposed emeralds will cut at a different rate. What you end up with
is an uneven cut and polish, and in some cases severe undercutting
of the softer parts.

If you need a volume filler, it is best to use the plastic pellets.
They are softer that any stone, but will carry the grit well. Just
make sure, that you never put used pellets in a finer grit than they
were previously in. Courser is OK. Keep the used pellets in marked
containers as it is hard to judge what grit they were used in.

A tip to separate the pellets from the stones. Get a large tea
strainer. Get a 5 gal plastic pail. After opening the tumbler
barrel, completely fill it with water and stir the mixture. The
plastic pellets will float to the surface and you can pour them off
into the strainer over the big bucket, keeping the stones in the
barrel. Do this a few times, and you will have all of the plastic
separated. Rinse each strainer full completely, and then, with a
sharp thump, upend the strainer on a layer of paper towels. This
will remove the cleaned plastic pellets. Make sure none of the
sludge goes down the drain unless you are planning on funding your
plumber’s kid’s college education and his retirement. Also keep the
plastic pellets out of the drain.

I would let the 5 gal bucket set and settle for a few days, and then
slowly pour off the clear water into the flower beds and lawn. As
soon as the sludge started to leave the bucket, stop. I then poured
the remaining sludge into some commercial cookie sheets I got at a
rummage sale. They were about 20 x 30 inches in size, and about 3/4
inch deep. If they were set on a level surface, they could hold
almost a gallon of sludge. When set in the California summer sun, a
pan would evaporate off dry in about three days. The remainder went
into the trash.



Marty - How large is your tumbler barrel? If you are using a pound
and a half barrel you won’t have to use much “filler”. If it is
larger than that, you’ll have to add more than the amount of
emeralds-in-matrix. Technically, agate is softer than emerald but
emerald is less durable due to fracturing and its crystalline
structure. I would use a non-stone filler like plastic beads, unless
the emeralds were really inexpensive, and you didn’t mind if they
got beat up in the process of cleaning them up. As far as grits go
you will need at least the three standard grits, plus polish.

Jim Small
Small Wonders


Marty, I have tumbled emeralds before. First make sure that your
emeralds are not of gem quality. I say this not because the tumbler
will ruin them, but because if they are of gem grade you should have
a lapidary saw them or grind them from the matrix.

You can use small agates to fill the rest of the tumbler. The
hardness is about the same. Make sure that the agates are the same
size as the emeralds or slightly smaller. I would use agates that
had already been tumbled to smooth edges. Start with medium 220 grit
and check the results every so often. Daily would be good in a
rotary tumbler and every three hours in a vibratory tumbler. Follow
it up with 600 grit, then a prepolish, and finish with cerium oxide
and a filler to cushion the load. You will have to clean the stones
very well after polishing as the powder will lodge in the cracks in
the material. You can clean the stones in a tumbler filled with
clean filler material and the stones using dish washing detergent and

Gerry Galarneau
G+LW Gem Mall Booth 111 Feb 1-14, 2003