Michael, Are the abrasives you refer to below already bonded to
a sanding disc of some sort? Or are they fluids that you apply to
a bare wheel (as on a lapidary plate)?
Tom, the answer is C: all of the above. In the “already bonded"
category, I use 8” discs on a crystalite flat lap machine; 2" wheels
on a slightly modified bench grinder ($20 at K-Mart - less than the
cost of one wheel); and an assortment of plated and sintered burrs
mounted in a point carver (a bit like a drill press lying on its
side). In the “fluids you apply” category, I have a few of the 8"
discs with fiber pads which I use for the later stages, i.e. 14,000
grit and finer; and the wood and phenolitic points which I use for
If the former, how long do they last before being too worn for
They don’t last near long enough given what they cost. The big tricks
to extending the life of a tool are 1) to keep it cool with water or
lubricant and 2) to let speed do the work instead of pressure. (More
about pressure and worn tools later.) Basically “your mileage may
And if the latter, how do you control splatter?
Splatter is not much of a problem with the “fluid” (which is really
paste - see below) approach. I do “rub” the grit into the tool before
turning it on. I have backstops/backdrops around all my machines to
catch the splatter from the water cooled tools. And I wear a very
dapper rubber apron – along with safety glasses, a respirator, and
You can get the “fluid” in a spray bottle, but what I use is actually
a paste containing diamond grit in a suspension medium (often some
form of oil). Generally speaking when using a diamond paste you do
not use water to cool the work, as in the “already bonded” category.
Instead you use an “extender” which is often some form of oil or
other lubricant. You can buy loose diamond grit and mix up your own
paste if you want a higher concentration of diamonds. There are
various mandrel/sanding disk combinations available, but I don’t use
them much. Wet/dry sandpaper is another option, and you can just cut
up a sheet of sandpaper and use the pieces by hand if you like. This
can be good for a larger carving.
In all of these configurations, the cutting tool stays in one place
and I bring the workpiece (the stone) to the tool. This is by
contrast with the originator of this thread (or rather her daughter)
who had the cutting tool in a flex shaft and was bringing it to the
work piece. By now I hope it is obvious that I do not facet. I carve
When I need aggressive stock removal and a saw, cut-off disk or
chisel won’t get the job done, I have some 80 grit tools which are
great. Otherwise I tend to prefer to shape with 180 grit tools
because the 80 grit produces a lot of chipping on the edges,
especially of quartz and other harder rocks. I find it takes more
time to get rid the chips than I saved during the shaping.
A few other pointers=85you do not need to use all of the grits, and
different stones will perform differently. My crystalite came with
180, 600, 14,000 and 50,000. This combination works for a lot of
But as I noted in my earlier post, on softer stones like turquoise
and mother-of-pearl you can often skip from 600 to polishing with
Zam. The “Advantage Polisher Kit” from Rio Grande also does a nice
job of taking scratches out of mother-of-pearl without leaving a
Other buffing, polishing agents work wonders on other stones as well.
Whatever your approach, you still have to get the scratches out
before you can get a polish to come up. I have some Siberian nephrite
which is fairly soft, around 6.0, and I go right from 600 grit to
green rouge (an ironic term to be sure) which will buff out shallow
scratches. This combination produces a smooth, warm, waxy appearance,
which I find appealing, whereas the finer grit tools either produce
the dreaded orangepeal effect, or no discernable effect at all. I
have some other, harder nephrite, which just ignores green rouge. So
I work up to 14,000 grit which gives me a glassy sheen/wet look,
which is all right if you like that sort of thing.
Last night I was working on a celtform in petrified palm wood. 600
grit brought up a nice gloss. 1200 grit produced a glassy sheen/wet
look. 14,000 grit caused undercutting on the “dots” leaving an
orangepeel effect. I ended up going back over the piece with 1200. The
mineral content of petrified wood changes from piece to piece so the
next piece of petrified palm wood will probably work differently.
I find I can get a glassy sheen/wet look on obsidian (although I
suppose any finish on obsidian is “glassy” by definition.) with a
modestly worn 600 grit wheel and a bit of pressure. I have also
gotten a similar result from a very worn (almost bare) 1200 grit
wheel that I ran with very little water (almost dry). Heat was the
polishing agent in this case and you have to be careful about heat.
It will fracture some stones and change, or even strip, the color in
others. I work with larger pieces and I find that holding them in my
bare hands (no dop stick) gives me better control and leverage. It
also makes it easy to feel the build-up of heat. If the workpiece is
too hot to handle, then it’s too hot period. Let a hot workpiece cool
slowly on a non-conductive surface. If you cool it too quickly, say by
quenching it in water, the thermal shock may fracture the stone.
My favorite dopping method is galvanized 2" roofing nails with either
gel super-glue or 5-minute epoxy. “Attack” brand solvent will loosen
the epoxy. Acetone will loosen the super-glue. Dopping is good if you
like having fingernails.
Keep your tools segregated by grit to prevent contamination. And wash
your hands and the workpiece between grits. Once you get a bit of
coarse(er) grit onto a finer grit tool or buff, you are going to have
to replace it.
I find it easiest to see scratches when the workpiece is clean and
dry. Bright lights and magnification are a big help too. Also, be
sure to rotate the workpiece as you look at it, some scratches are
more obvious in one orientation than another. Sometimes the glossy
finish can make scratches hard to see and I find it pays to look just
"past" the gloss at the surface itself. When the workpiece is nearly
finished in one stage but there are a few patches left to touch up, I
mark them with a Marks-A-Lot or a Sharpie. This makes it much easier
to relocate each patch once the workpiece is wet and the marker ink
polishes right off with the scratches.
Hope this helps,
President, Conlin & Associates