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Scuffed cab

Hi Folks…

About 10 years ago, I set a fire agate cab in a Donello type silver
preset…Is the brown Mexican type with the colored bubbles that
display in brighter light…The reason it stuck me was the variety
of colors displayed…Green, blue, orange brown, yellow and even
some violet…It has rocked folks when they notice what it does…

I was lucky to find the critter in an almost 18X13 calibrated size,
low dome…That’s been my personal ring ever since…

I’m hard on jewelry, that I wear, mostly because I’m a clutz…

This is a type of quartz stone and has proven surprisingly durable
for me…It appears to have finally gotten itself scuffed…No deep
scratches under magnification, just lots of little ones…

I’d like to try to repolish it myself, and have at hand a variable
dreml tool and buffs…And lots of time and patience…

I suppose it would be best to ask around and have someone local do
it, but it’s the kinda thing where I’ve got my hand in it…Working
metal is mostly what I’ve done…The only stone polishing I’ve done
was with a rock tumbler as a kid…

Any advice…

Gary W. Bourbonais
L’Hermite Aromatique
A.J.P. (GIA)

About 10 years ago, I set a fire agate cab... for me...It appears
to have finally gotten itself scuffed.... I'd like to try to
repolish it myself, and have at hand a variable... dreml tool and
buffs...And lots of time and patience... Any advice.... 

Gary, while you could try to polish it yourself, I’d stronly suggest
otherwise. Find a cutter who’s got some experience with fire agate.
It’s not just an ordinary piece of quartz or agate. The “:fire” is
due to a layered structure, with irridescence coming from imbedded
thin layers of limonite. To get the proper effect, the cutters have
to carefully follow the contour and depth of these layers. Cut just
a little too deep, and the whole pattern can change or worse, the
fire totally disappear. Plus, that layered structure can make these a
bit tricker to polish than most other agate, which is generally easy.
While you might well be able to do a fine job with your Dremel,
That’s kind of a bare bones minimum and not very adequate tool, and
you have not got lapidary experience, especially with fire agate.
Doing it yourself you seriously risk ruining the stone. If you don’t
mind that, of course, have at it. Easiest is a prepolish with a fine
diamond compound, perhaps a 3000 grit, using something like a wood
lap (make your own from a short cutoff of a hardwood dowel) for the
dremel, run at slowest speed). This would be enough if the scratches
are fine enough. Then buff either with 14K diamond on a small felt
wheel, at medium speed, followed optionally with the same only with
50K diamond; or with something like a cerium oxide slurry, also on
felt or muslin wheels (use damp). Perhaps you’ll do a fine job and
get a fine new polish. But if you crack it, or find the colorful
pattern has changed or diminished, don’t say I didn’t warn ya.

Peter Rowe

Practice, practice, practice on something you don’t value before you
try the fire agate. Recutting and polishing the cabochon should
actually best be done with a lapidary unit. If you don’t have one,
someone near you may. Check to see if there is a Gem and Mineral
Club near you, many have workshops that have the equipment for
cabbing and folk with a lot of expertise in cutting/polishing them.
As with any stone, there is the possibility that the agate will
break, and/or look worse after being redone than before.

Yes it can be done with a dremel unit, just very difficult to do.
Can also be done by hand with emery paper and leather/felt with
diamond polishing compound or even cerium oxide polishing compound.

Good luck.
John Atwell Rasmussen, Ph.D., AJP


I would try diamond paste polishing compound on your rotary tool.
Start with the largest size diamond grit and work your way to the
smallest (Usually from 300 to 50,000). Use separate polishing wheels
for each step.

Here’s a link to a set on diamond paste in syringes.

Rick Copeland
Silversmith and Lapidary Artisan

Hi Gary,

I to fell in love with fire agates back in the 70’s when I started
making jewelry, in fact I’ve been wearing a ring I made in 22 karat
yellow gold since 1998. The stone is a free form cab that I cut
about ten years before setting, only because I wanted to know so much
more about silver and goldsmithing. I strongly suggest that if you
can, take the stone out of the setting, you’ll be ahead of the game,
as you’ll be able to mount it on a dap stick, or epoxy it to a large
nail head to be able to get to all the scratches around the sides.
These agates are 7 1/2 to 8 on the hardness scale so you’ll have to
use diamond wheels to make your life easier. You’ll want to have
diamond powder with wool buffs and Vaseline for the final polish,
just coat the felt wheel with a small amount of Vaseline then
sprinkle some 5000 grit diamond powder on it to start, you may have
to go up to 15000 grit for the final polish followed by some cerium
oxide and leather. You probably only need to use 600 grit diamond to
take out most scratches but have some 320 if the scratches are deep.

Good luck, the process is easier if you can see a book that explains
the lapidary side of polishing stones.


These agates are 7 1/2 to 8 on the hardness scale so you'll have
to use diamond wheels to make your life easier. 

No. They are 7. They are cryptocrystaline quartz, as is all agate.
Tougher than single crystal quartz due to the interlocked crystals,
but toughness is not hardness, and it’s still a variety of quartz,
and quartz is the defining mineral for mohs hardness of 7. So they
are not a 7.5 or an 8. They are 7. An agate could be higher on the
hardness scale if it had significant percentages of included mineral
mixed in that had a higher hardness, but that’s very unusual (if
indeed there are such things. I can’t think of one.) In the case of
fire agate, the primary inclusion is layers of limonite, which is
softer than quartz. Many agates may seem harder than single crystal
quartz when grinding them, but again, this is a matter of the
increased toughess imparted by the structure. It’'s not an increase
in hardness.

However, the suggestion to use diamond compound is generally
correct, since the differing hardness of the silica layers and the
limonite layers make a good glossy uniform polish sometimes more
difficult with oxide polishes. But only sometimes. The main advantage
of diamond compounds is simple speed, and that they pretty much work
as well with almost anything.



Thanks for all of the warnings and advice…

Probably look up some lapidary folks…

Feel suddenly more wary…

Gary W. Bourbonais
L’Hermite Aromatique
A.J.P. (GIA)