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Polishing hard stones


#1

Hi all: We need some help from the ‘stone people’ for a beginner (my
daughter) who is just beginning to carve stones and who is asking me
questions I can’t answer. She is using a flexible shaft, diamond
powder, and some premixed diamond powders of various grits. So here
are the questions:

  1. When polishing a stone like a small, rough emerald, with a
    flexible shaft, in what order should the grits be used and what kind
    of buffs? How would it differ from polishing softer stones?

  2. How do you determine when to move on from one grit to the next
    level and how long should it take (all day?) for the final polish.

  3. What is the best book for beginners who are essentially self
    taught (she has an MFA in printmaking, but this is her first attempt
    at stone carving–and she loves it).

  4. Any other help or advice would be greatly appreciated. I will
    send it all on to her, and in the process learn something myself.

Sandra B.
elegant insects @aol.com


#2

Sandra B. Wow, you pose the questions ever novice asks. And they can
be answered but it takes plenty of space and time. Rather than do
that here, suggest you go to the Lapidary Journal or Rock & Gem web
sites and do an archive search. There have been some terrific
articles over the past few years that address the use of diamond
tools in carving. There are also many books on the subject. One
that is very nice is ‘Handbook of Gemstone Carving’ by Ed and Leola
Wertz , published by Gembooks of Mentone, CA. My edition is 1968
but I’m sure there must be later editions. Nice to see someone
trying their hand at a very fascinating hobby…or profession as the
case may be. Tell her to stick with it. Cheers, Don at The Charles
Belle Studio in SOFL where simple elegance IS fine jewelry.
@coralnut1


#3

Sandra - I highly recommend LAPIDARY CARVING FOR CREATIVE JEWELRY by
Henry Hunt to provide the answers to your daughter’s questions. As a
lapidary procedure, carving partakes of general lapidary knowledge
plus specific carving knowledge and techniques. Hunt’s book helps
integrate the two very well!

Jim Small
Small Wonders


#4
Hi all: We need some help from the 'stone people' for a beginner
(my daughter) 

The first thing you shoud do is get your daughter a good quality
respirator, the kind with cannister filters, not the throw-away fiber
masks. Lapidary carving, especially the later stages of polishing,
puts fine particulate dust into the air and she’ll need protection
from that.

Make sure she has, and wears, safety glasses each and every time she
carves. Safety glasses are not optional.

1. When polishing a stone like a small, rough emerald, with a
flexible shaft, in what order should the grits be used and what
kind of buffs? 

Start with the coarsest grits and work toward the finest. The smaller
the number, the coarser the grit. So the process is: 60, 80, 180,
325, 600, 1200, 14,000 and 50,000 followed by tin oxide, cerium oxide
or similar compounds. Many carvers put the diamond grit onto wooden
points and wheels which they shape to the task. Phenolitic points and
wheels are also available from suppliers like Kingsley North.

With harder stones you have to go through the entire sequence to get
good results. But with softer stones, it isn’t always necessary. I
find that on turquoise I can often go right from 600, or even 325 if
I am careful on this stage, to a final polish with Zam and a cotton
buff.

Also, finish can be a matter of taste. For my taste, mother of pearl
and nephrite both look like plastic when taken to a glassy, high
gloss. Sometimes turquoise, even untreated turquoise, does as well.
On the other hand, jadeite, mahogany obsidian and emerald benefit from
a high gloss.

2. How do you determine when to move on from one grit to the next
level 

You move on when all of the scratch markes from the previous grit are
gone. And be careful to clean the stone and your hands in between
changes in order not to contaminate the finers grit.

and how long should it take (all day?) for the final polish. 

Allow an hour or so per piece to get from rough to polished,
depending on size.

    3. What is the best book for beginners who are essentially
self taught. 

Get a copy of Henry Hunt’s “Lapidary Carving for Creative Jewelry”,
ISBN 0-945005-10-5. It’s a little dated in stylistic terms, but the
technical advice is excellent. Also, get a subscription to Lapidary
Journal. Or better yet, get your hands on back issues if you can.

Finally, don’t neglect the Orchid archives. There have been many
discussions of the best way to polish this or that stone.

Michael Conlin


#5

Sandra, in general you want to go from the coarsest grit to the
finest (the lower the number the coarser the grit) she should also be
using different buffs or wheels for each grit. These should also be
kept separate to prevent contamination between the grits. Without
knowing exactly what she has available to her it is hard to say what
she needs to be using. As for when to change to a finer grit you
should always get your stone as smothe as possible with the grit you
are using for example 100grit rough shaping, 220 smoothing and
removing ridges, 600sanding should have a pretty smooth scratch free
surface, 1200 pre polish should be taking on a satin to low shine. At
this point you can go in to a finer pre polish or polish depending on
the stone and polishing materials avalible to you. The polish is only
going to be as good as your previous steps will allow. For example if
you have scratches when you leave 1200 you will have scratches in
your polish. Theoreticaly you could eventually polish them out but
yes then it would take all day. For polishing I normally use 3,000
then 8,000 then 14,000and finally 50,000 diamond. Sometimes I will
skip some of these on softer stones. And on rare occasions will use
some of the oxides avalible. I stop polishing when the stone take on
a perment wet look or mirror finish. Also between each step you
should clean and dry the stone to inspect it. Watter and oils will
hide scratches. I know this is pretty general but with out having
more on her equipment kinda hard to give specfics. If you
need more please feel free to contact me off list either
by email or phone at my store I am open m-s 10-6 east coast time.
Joseph Martin Genesis Jewelry @Rockhead1 828-635-0293


#6

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)? If the former, how long do
they last before being too worn for use? And if the latter, how do
you control splatter? (This is NOT supposed to be a poem ) I think
I’ll invest in the book you reference (I’ve got way too many
questions) too. Thanks, Tom


#7
    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
all stages.

 If the former, how long do they last before being too worn for
use?  

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
vary”.

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
hearing protection.

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
and cab.

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
stones.

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
plastic appearence.

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,

Michael Conlin
President, Conlin & Associates
1-703-391-2521