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Fix scratch on agate cab

I’m hoping someone can direct me here.

I was setting a tube-set faceted stone into a beautiful pale-yellow
banded agate cab. The cab is nicely polished, of course.

My diamond bit jumped out of the hole I was drilling and skittered
about 1/4" across the surface of the cab, leaving a wonderfully
visible little scratch on the surface.

I’ve tried the various sanding surfaces I have handy (sandpapers),
and none seem to affect the cab surface at all. So before I go
further an ruin this thing in its last stages of assembly into a
pendant, can I get some direction from those of you with experience
at this?

What abrasives do I need to first sand out the scratch and then
repolish the area on the cab? (Thank heavens it’s a flat-top, so I
don’t have to worry about matching curvature.) I should mention that
my “lapidary” experience is limited to drilling holes in various

Thank you!
Karen Goeller
No Limitations Designs
Hand-made, one-of-a-kind jewelry


Since agate is relatively hard it would be best fixed by a lapidary.
I would be happy to do it. Contact me off list and I will give you my
USPS address.

Rick Copeland
Silversmith and Lapidary Artisan
Rocky Mountain Wonders
Colorado Springs, Colorado

You did not say how deep the scratch is. I do not know if you have
access to a lapidary machine (grinder). Nor do I know how far the
stone (top) is above the surface of the mounting; it might be best if
you could take the stone out first, or may it won’t matter if
careful. This article may be of some help in what is to be said next.

This could be done by hand, be advised that agate is one of the
hardest materials, so this will take some time. If you opt for
sanding get wet-dry, and get the kind suitable for auto body repair,
silicon carbide, and use wet. The incorrect choice may be the
problem, but of course this is a sand, sand, and sand thing, also. In
any event, either with a wheel (of a cabing unit) or sand paper,
start with a 100 to 150 grit, until you can not see the scratch, next
a 200-250 wheel (or sand paper), next a 600 sand (some go 400 then
600, not nessasay, but would mention it). At this point it should be
suitable to buffing with Cerium Oxide (the usual choice, tin oxide
would work, zam is useless for stone of this hardness). The
importance of the final fine sanding is the single most important
part of getting a high polish. There should no visible scratches at
all. If you see scratches, when beginning to polish or the surface is
not smooth go back to sanding.

Now what has been said has some caveats, now what has been said
applies to using silicon carbide grinding wheels, followed by, If you
are using silicon carbide, 600 grit sandpaper on a drum or disk. This
wears fast, it becomes finer grit (mixed, as breaking down in use),
and it is all you need for a pre-polish. (If using sandpaper, by
hand, you may want to go with 1200 next, after 600).

If doing this by hand, use a flat surface, maybe a sheet or two of
paper as pading, tape the sand paper to this surface, providing there
is good clearance between the mount and stone it may actually help to
leave it in, easier to hang onto while doing it.

If using diamond equipment (such as a Genie) just start with the
first wheel, the second etc., by the last it will be finely polished.

This can be done also with a faceting machine, use a course lap
until the scratch goes away, and a finer (medium, maybe 600) lap,
1200 diamond is a fine pre-polish for agate (polish) and of course
you can use a lap above 1200, maybe 30-50,000 to polish it.

It would be possible to use other equipment, flex shaft (orchid has
a step by step article on how to make a turquoise cab with a flex
shaft). Or for that mater, even a drill with the right sanding
disk(s) or drum(s), and a buffing wheel loaded with a polishing
compound, but as this is a flat top you will have to use care (much
more, with this smaller diameter equipment), to insure it stays that


I’m sure you’ll get better answers for this but if I were doing the
repair the depth of the scratch would define the grade of abrasive.
If it is not very deep you might try starting with 1200 grit and then
polishing with 14,000 diamond. If 1200 doesn’t work go down to 600.
Also, are you doing the sanding by hand or with a Lapidary machine?
By hand will take a good bit of work.



Thank you for taking the time to reply and for your helpful
suggestions. I will be doing the work by hand or with my flexshaft
(if I can find the right grits for it). The scratch isn’t very deep,
so I may try it myself and if that doesn’t work, send it to a
lapidarist to have them fix it.

No Limitations Designs
Hand-made, one-of-a-kind jewelry


Unfortunately, it not as easy to fix a scratch as just sanding it
out and polishing.

It is important to know how deep the scratch is so you can decide
what abrasive to start with but, there are many other things to
consider. For instance, it is difficult to scratch a polished agate
(Mohs 7) with a bezel roller/burnisher (Mohs 5.5). Check the
’scratch’ very carefully. Is it really a scratch into the surface or
just a mar across the surface? If the latter, a bit of cerium oxide
on a piece of soft leather dampened with water may remove the mark.

Otherwise, if the scratch is through the original polish and the
stone is set, you probably would only be able to get to the top most
part of the cab. Unfortunately (another one) is you can rarely sand
and polish just one area on a finished cab and get a good looking
fix. It will always show a demarcation line between the original
cut/polish and the new.

So…I would recommend removing the stone, smooth sand the entire
cab and polish over. If the scratch is not too deep, you can probably
get away with 1200 grit, either diamond or silicon carbide paper
paper with water will do. You might be able to do this by hand if you
take your time and it will not change the shape or geometry of the
stone. By the time you are finished with the 1200 paper the stone
should be quite smooth…if not go to a 3-8000 paper.

To polish, you can get away with a soft felt wheel on your polishing
lathe. Add a bit of wet cerium oxide polishing compound to the wheel
and firmly hold the stone to the wheel turning it in all directions.
Be careful, the wheel will try to pull it away from you. Add a spritz
of water now and then to keep the wheel damp. When satisfied, reset.

Hope this helps. Cheers from Don at The Charles Belle Studio in SOFL
where simple elegance IS fine jewelry!

I've tried the various sanding surfaces I have handy (sandpapers),
and none seem to affect the cab surface at all. So before I go
further an ruin this thing in its last stages of assembly into a
pendant, can I get some direction from those of you with
experience at this? 

Any faceter would have the flat laps for this job. If it doesn’t
need to be removed from the mounting (or if you remove it) it should
take only minutes. The exact technique would depend on the depth of
the scratch, but I’d guess 600 diamond, 3000 diamond, then Cerium
Oxide polish.

What abrasives do I need to first sand out the scratch and then
repolish the area on the cab? (Thank heavens it's a flat-top, so I
don't have to worry about matching curvature.) I should mention
that my "lapidary" experience is limited to drilling holes in
various stones. 

Al Balmer
Sun City, AZ

Most lapidaries will probably need to go back to a 320 grit diamond
belt ( for flats a faceting disc would be best if available) and
resurface the whole flat top. Then the usual steps would be a 400
and 600 belts. After this I just go to cerium oxide on leather buff.

Larry E. Whittington

Dear Karen,

As you may have noted I was trying to get you to do-it-yourself.
Actually once you saw how easy and quick that kind of repair is
(based on what you said off list) I think you would be surprised.
That could also be done by hand it wouldn’t be hard, it would just
take some time.

If all else fails, although I did not want the responsibility, write
me off list, I could fix that (free), if you pay postage. That
scratch would take but a few minutes, I have a diamond unit at home.
I still think it would be best to drop into a class if you could, to
see how it is done. “I don’t have access to any lapidary equipment
(I’ve tried to resist that potential source of addiction).” Actually
if you notice the price difference in cutting rough and finished
stone you would understand why people cut, but yes it is addictive.
In any event, even if you do not want to learn to cut, I think it may
be important to know how at least to sand and re-polish in the event
this (or some such thing) ever reoccurs. It is not as hard as it may
seem. You mentioned you touched up a stone sometimes with zam and
your flex shat. That (zam) is great for turquoise and many stones, it
will not properly polish agate, quarts, jasper and stone of that
hardness, hence my mention of cerium oxide, and some prefer tin

As you have a flex shaft I think you may find this article of

I will say this again for the benefit of anyone reading this, I see
from time to time a question on how to get started, my advice to all
is, if available, contact the nearest gem and mineral club near you.
Most have or are connected to a shop/class. (A few, not most also
teach faceting, the Old Pueblo Lapidary Club is one that dose. They
have a faceting CD you can download free.) What are the advantages?
No tools, equipment or experience needed, they will show you how.
Before anyone snubs this, you would be surprised at what some make,
and although I can not speak of all, the Golden Spike, Ogden, has a
more than one member who owns a “brick and motor” store. Besides you
might have some fun. And you will learn something, quite a bit.


I’m usually game for taking the DIY route, and likely will with some
other pieces. For this one, with a show that starts tomorrow, I just
literally didn’t have the time to spend finding the right
materials… I’ve already “written off” the piece being ready for the
show, which is a major bummer to me, as it was one of a new line that
I’m debuting.

I would like to try it in the future when I have a few brain cells
and minutes to spare. I just have been resisting anything that is
"too lapidary" at this point, to help me manage my focus on
developing my skills. I tend to get too scattershot if I don’t
discipline myself… “oh, look, I can try THAT next!”

I really do appreciate your generosity with the info and advice!

No Limitations Designs
Hand-made, one-of-a-kind jewelry