Tumbling obsidian

Jewelry Discussion
1

does anyone have any ideas on how to get a good finish on
obsidian/apache tears in a tumbler. We do fine by hand with
cerium or tin oxide but nothing seems to work in either a
vibrating or rotary tumbler. We’ve tried it with leather patches,
parafin and plastic pellets, all with the same poor results. Any
other ideas? thanks, Martin Freed

2

< does anyone have any ideas on how to get a good finish on
< obsidian/apache tears in a tumbler. We do fine by hand with
< cerium or tin oxide but nothing seems to work in either a
< vibrating or rotary tumbler. We’ve tried it with leather patches,
< parafin and plastic pellets, all with the same poor results. Any
< other ideas? thanks, Martin Freed Martin,

We tumble- polished successfully Fire Opal using 50,000
diamond powder and rice grains…try this and let run for 5-6
days. you need at least 10 cts for 2kg load. if you see any
improvment ,let it run longer if it is not too expensive use more
powder.

Hemi Englisher, GemCal Co. 21/6 Rajple 2 Cha-Am, Petchaburi 76120
Thailand.

http://www.ganoksin.com/kosana/gemcal/spinel.htm
Fax # 6632 434015
Tel # 661 4457742

3

hemi-Englisher wrote," we tumble polished opal using rice…"

One must assume the rice was dry??! I have a tumbler going in
the basement right now, it’s been going for a week, and all
that’s happening is it’s polishing the edgeds of stuff. It has
the plastic pellets you buy,a bit of water, some little chunks of
styrofoam, and of course the polishing grit. What am i doing
wrong here? I want to be able to rough out stones on my diamond
wheel and finish in the tumbler, but this just ain’t working for
me… A. Stickney

4

Try some different media. The plastic pellets probably aren’t
rough enough to cut the obsidian; you will probably need
something like a ceramic cutdown media first, followed by a
polishing medium like the plastic pellets, then fine polish with
walnut shell.

5

Plastic, rice or Styrofoam all should be dry. we must remember
that tumble polishing is a step by step process. if one of the
steps is not absolutely completed ,the next one will never be
perfect. check out your procedure. try Diamond powder. it is fast
. Please find here an old text ihad send to Orchid some time
ago, you may find some hints there. feel free to contact me
agaim…

Hemi.

       U S I N G     V I B R A T I N G      T U M B L E R

A. THE MEDIA. B. THE POWDERS C. LOGBOOK D. THE MACHINE.

A. THE MEDIA.

Media is the material that used with the stones. it must be the
same hardens as the stone we polish. the best is to use the off
cuts of the same material. for example Amethyst cabs with
Amethyst off cuts.

Please Note:

  1. the average size of the media must be close to the size of
    the stones. 2. if you do various sizes at the same time, you must
    use close sizes, e.g. 4x6 5x7 or 8x10 10x12. do not mix size that
    are too different like 6x8 with 13x18. the total wight of the
    media and the stones should be around 3 kg. the should be around
    40% of the total.

the best indication for the polishing action is to see a fast
movement, or quick turning of the media in the machine. if it is
too slow, something is wrong.

  1. the media is too wet(too much water).
  2. excessive wieght.
  3. not enough wieght.

the media should be semi wet, like mud.water should be added
when it gets dry.

when every phase of the process is done, the media should be
washed, and the powder should be kept for the next round.

B. Powders.

good news for you!! we use Silicon Carbide or Carborondom(?).

  1. run SC # 220, 25gms for 15 hours. add water when needed.
    check the surface of the stone every few hours.

  2. run SC # 360 40 gms for 24 hours. add water.check surface.

  3. run SC # 600 40 GMS for 30 hours . " " " " .

  4. run Diamantine 20 gms 30 hours . " " " " .

  5. rinse with water and light detergent for 1 hour.

the media the stone and the container must be washed carefully
after every run.

THE MOST IMPORTANT THING IS TO KNOW WHEN THE STONE
IS READY FOR THE NEXT PHASE. YOU SHOULD CHECK THE
SURFACE OF THE STONE AND MAKE SURE THAT IT HAS A
UNIFORM TEXTURE! IF SOME PARTS OF THE STONES ARE
DIFFERENT YOU MAY HAVE TO REDO IT.

PLEASE NOTE!

THE ABOVE NUMBERS WILL CHANGE FROM ONE TYPE OF STONE TO THE OTHER!
THESE NUMBERS ARE GOOD FOR CITRINE, AMETHYST. IF YOU POLISH ANOTHER
TYPE, YOU MUST FIND THE QUANTITIES USING A…

C. LOGBOOK

It is very important to keep a logbook of your production!
you should write all the details. hours, weights of powder, wieght
of media, if you do not keep this book, you will have to find the
way every time…if you doing new type of stone, you can compare
each run and make the necessary changes.

D. THE MACHINE
you can change the amplitude of the vibrations by changing the
position of the wieght on the motor axle. for smaller loads,
you need lower amplitude.

Hemi Englisher, GemCal Co.
21/6 Rajple 2 Cha-Am, Petchaburi 76120
Thailand.

http://www.ganoksin.com/kosana/gemcal/spinel.htm
Fax # 6632 434015
Tel # 661 4457742

6

A method I have had good success with for tumbling obsidian (as
well as similar hardness materials such as opal, goldstone, and
sodalite) is to mix the charge 50/50 with limestone (or other
scrap calcite based material). I use the limestone filler with the
obsidian through all the steps. Just make sure the limestone
chunks are initially a bit larger than the obsidian because of
it’s faster wear rate.

Gary VanGelder

@GaryVG