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Cabochon polishing


#1

I need to add a good polishing setup to my lapidary workshop. I am
self taught and have just been figuring things out from old books
and as I go. Polishing however has been the sore spot. I have used
both diamond and traditional compounds with success. It has come to
the point where I need a defiant polishing station, no more changing
belts. Do I go with diamond, does it polish everything or am I
better off with a dual arbor and more traditional compounds? I was
looking at the Graves spool polisher or a dual arbor setup. Any
suggestions would be greatly appreciated.


#2

Phil - I don’t know that there’s a simple solution for your woes.
I’ve been cutting cabs for almost 45 years now, and I use a variety
of equipment. The one piece which I’ve tried and gotten rid of was a
spool polisher; not because it didn’t work, but because other pieces
of equipment worked just as well. I do my cutting with this
combination: roughing in and coarse grinding with diamond on hard
metal wheels; all phases of sanding on 8"x3" silicon carbide belts;
final polishing on a slow speed flat lap. I also use polypads with
diamond compound for some sanding and polishing, and I have several
different nifty gadgets for stuff like star stones. I have found my
hybrid setup does the best for me. I hope this helps you, some. I’m
certain the Gerry and others will share their own experiences.

Jim Small
Small Wonders


#3

Hi, Phil-

If you find any substance which polishes everything, pass the news
on- I for one will be grateful. My current experience is that
different compounds work best for different materials. I like tin
oxide and/or cerium oxide on leather for agates and jaspers. For
matrix opals, I am sometimes faced with a wide range of
hardness/softness and porosity in the same stone, with components
ranging from hematite to (barely) vitrified clay. Super Polish from

http://www.mtmist.org/ttom.html

can be a secret weapon. Sometimes.

No one approach works for all rough. Diamond tends to minimize
undercutting. White Diamond and/or Zam sometimes tends to harden up
a softer matrix, and bring out the polish in materials like
partially silicated chrysacolla and some Yowah opals-- but no
promises. For plumes and more porous agates and jaspers, cerium
oxide gives a great surface polish-- but is a cold-hearted bastard
to get out of the little pits and blems in the agate. (on this last
issue, removing polishing compound from pits or blems, fellow
Orchidians please consider this a cry for help- I have some very
nice included agates which I cannot currently rid of embedded
polishing compounds.)

My best advice is to identify the materials you most like to work
with, and learn the polishing protocols which best suit them.

Lee Einer


#4

All, I agree with Jim Small on the methods of polishing cabs. My own
set up is modified to have rough sanding to 220 grit on silicon
carbide belts then finished sanding on resin pads charged with 600
diamond, 3,000 diamond and 14,000 diamond. All my polishing is done
on either 50,000 diamond or cerium oxide and felt.

For my resin pads I use hard back spin discs for the backs of the
cabs and sponge rubber backs for the crowns. Spin discs are adapted
to shafts using shaft adapters available from many different
suppliers.

Diamond compounds are not all created equally. My suggestion is for
you to try many different manufacturers of diamond compounds until
you find the one that works for you. Diamond compounds depend upon
both the carrier that the diamond is mixed in , the concentration of
the diamonds, and the quality of the diamonds. I buy my diamond
compound from a manufacturer that sells only in 25 gram tubes and you
must buy $500 USD at a time. Most of you would not be interested in
such a buy.

I am going to remodel my shop this summer and set up numerous motors
with spin discs. I am going to use two speed motors that spin at
1725 and 3450 rpms. I want to try the higher rpms using diamond
compounds. For oxide polishes I have no problem at 1725 rpms and
would not try 3450.

Some of the best polishes on hard agates I have ever seen were made
using leather and aluminum oxide at very slow speeds. The man doing
the polishing did not tell you how he arrived at that stage. He was
flame prepolishing at 3450 rpms on a used 600 belt. Very dangerous
to the cabs and the person using the equipment, but the results were
fantastic.

I use my a Pro Sonic machine with dish washing detergent to clean
the polish caught in cracks. A good way to avoid this problem is to
coat your cabs with super glue prior to your finish sanding. Sand
the cabs down to prepolish and polish the cabs. Soak the polished
cabs in acetone over night and the super glue dissolves. A little
time consuming, but no residue in the natural cracks and crevices.

Happy polishing, 12 days to Tucson and what a mess.

Gerry Galarneau
Tucson G+LW Gem Mall Booth 111 Feb 1-14, 2003
www.galarneausgems.com
@Gerry


#5
I have some very nice included agates which I cannot currently rid
of embedded polishing compounds.) 

I’d suggest a good quality ultrasonic, with BCR cleaning solution.
BCR stands for 'buffing compound remover"… Mix it up pretty
strong., use it quite hot, and if needed, leave the stones in there
for a while. Obviously, this isn’t good for the softer more fragile
materials that could be damaged by an ultrasonic cleaner, but your
agates should be just fine. If needed, for extra ooomph, add some
additional ammonia.

And, though I’ve not tried this, I note that many of these compounds
are metallic oxides. Cerium oxide, chrome oxide, iron oxide, etc.
It occurs to me that you might try some fresh pickling acid. Perhaps
made from actual sulphuric, or other acids, rather than the safer dry
salts usually used. The silica gems, like agates, shouldn’t be
affected, at least not by a brief soak. I’ve no idea whether this
would work, but it should be worth a try. I’d not leave plumes in
there long, though, since of course the patterns in the gem are also
sometimes iron oxide based, which might also be attacked if you
leave the gem in there too long. but those are imbedded in the
stone, while the polishing compounds should be more quickly reached
from the surface. And if this seems to have some effect, but not
what you want completely, then after rinsing off the pickle, put it
back in the ultrasonic…

Peter


#6

Hi Lee,

I have some very nice included agates which I cannot currently rid
of embedded polishing compounds. 

Ultrasonic doesn’t work? It does for me.

Beth


#7

Phil,

Your question is not an easy one to answer. A lot depends on what
kind of stones you are cutting…opal, turquoise,
agate/jaspers/quartz, corundum, etc? Also, are your cutting smaller
geometric, large, freeform, retro-cut? Mostly flats, high cabs, low
dome cabs?

For your consideration, I cut a variety of material, sizes, and
styles. For many years I used a homebuilt flat lap but when I began
cutting more and more, lap changing became a chore so I purchased a
modern 6 wheel combination grinder/polishing unit. It happens to be
a GemTec (no affiliation …just happy user). It has two hard
diamond grinders, two Nova diamond smoother ‘soft wheels’ (280 and
600), a Nova 1200 pre-polish and a 50,000 Nova ‘polisher’. It also
has changable end plates for either diamond pads or powder based
pads. I find the 50K polisher does a nice job but I always finish my
cabs with a powder - cerium, aluminum, or other oxides on felt or
leather. There are other combo units avail…Pixie, Graves 6
Wheeler, etc but, a nice feature about the GemTec is a DC motor
which allows total speed control from 0-2000RPM. Thus, I can
correctly cut at high speed and dial down to low speed for polishing.
While this is an excellent machine and takes quite a bit of
punishment, I doubt it would hold up to production cabbing such as
Gerry or some others do. Any of the combo machines would do the
general jobs and take up less space and do everything at one
station.

Back to part of your question. Some time last year, there was a
long discussion about using diamond or powders for polishing. We had
some great input on various theories and procedures. I still owe the
group a paper on the polishing theory that oxides excite an
electrical response on the surface of stones that causes the
polishing action. Most agree however, that there is a resulting
plasticity (not the old Beilby theory) on the stone’s surface that
causes the high polish. In my own opinion (subjective only) diamond,
being an abrasive at any grit, does not create this reaction. I
always see a diamond polished cab as being slightly ‘greasy’ while
those done with oxides seem more pure. I recommend using oxides…on
various carrying mediums.

Oh boy, here we go again…Sorry folks!

Cheers from Don at the Charles Belle Studio in SOFL where simple
elegance IS fine jewelry! @coralnut1


#8

Hi Lee, I have found that in some instances, where an ultrosonic is
not effective, with the addition of steam, try putting your stones
(not heat sensitive, of course) in an ammonia, soap and water
solution and bringing it to a boil in a micowave oven (or on a stove
top, but the microwave is so convenient). This will often dislodge
the most stubborn materials. Good luck!

John