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Polishing inlaid malachite

#1

More regarding polishing inlaid malachite. This evening, having
sufficiently recovered from a terrible 3 day cold, I went out into
my shop and was rooting around looking for something to do. I came
across a bag of malachite that has been there for the past 20 years
or so and decided to cut a piece. I did so and finished a beautiful
52x43 freeform cab. Then, before leaving, I took a small extra piece
and tried some things with it. I gave it a semi-polish up to 600 and
then turned off the water. I held it on hi speed until it was to hot
to hold. Nothing. Then I moved to the 1200 and continued to press
into the wheel dry. Nothing. Finally, I went to the 14K and had the
same result - nothing…no oxidation, no nothing but a nice smooth
and polished surface.

So, I went over to the ZAM, loaded up the buff, and polished it hard
till I could hardly hold it. Nothing, no oxidation, no blackening, no
crumbling, nothing! I found nothing wet and nothing dry that would
explain the problem the member described. Nor have I ever came across
the problem as described over years of cutting malachite. Comments
anyone?

Cheers from Don in SOFL.

#2 
I found nothing wet and nothing dry that would explain the problem
the member described. Nor have I ever came across the problem as
described over years of cutting malachite. Comments anyone?

Perhaps reconstituted malachite?

Richard Hart G.G.
Denver, Co.

#3 
Nor have I ever came across the problem as described over years of
cutting malachite. Comments anyone?

Me either. I think she found an inclusion or other defect within the
stone, and was merely unlucky enough to polish down to it. That, I
have seen now and then…

Peter

#4

Dear Don,

I have some malachite from Zambia that is a nice solid material that
you can do anything to as you describe. I also have some more
fibrous material from a wholesaler in the UK, original source
unknown, that burns to a black when you apply friction to any degree.
Difference between the two? well, probably minute amounts of azurite,
which is hydrated and the loss of water probably causes the different
behaviour. I treat the 2 materials differently because they behave
differently. Same goes with my Wello opal, it is not the same as my
australian stuff so I dont treat it the same way. I’m going to facet
some of the really transparent jelly to see ifthat takes advantage
of its hydrophane properties.

Nick Royall

#5

That was my guess also, reconstituted.

Hans Durstling
Moncton, Canada

#6

Nick, HHHmmmm, sounds interesting. Are there any identifying
characteristics that might indicate such a difference between the
two malachites? Such as slight blue coloration, lighter/darker bands,
softness, etc? In fact, the stuff I worked on the other night appears
more fiberous than chalky. It was dark with narrow lighter bands in
it. On the other hand, I have cut many malachites with azurite in
it…like areas of more bluish than others kind of like the mixtures
one encounters in chrysocolla but still never encountered what was
described. What happens when it turns black? When you apply it to the
wheel does it turn black with water or dry? Is it permanent or is it
wiped away.

Cheers from Don in SOFL.

#7

Again, in my experience…

Malachite is extremely variable stuff. Some pieces are less
sensitive than others. You can cut two cabs from the same slab and
one of them will work up just fine while the other one is nothing but
trouble.

RC

#8

What really threw me off was that the two stones had gone through
the entire cutting and polishing process before they were set and
there was no indication of a problem. Two of us tried to replicate
what happened like you did Don and no black spots. We didn’t think
it was reconstituted but Nick it doesn’t seem like it was Mother
Nature’s best chunk of Malachite. I think Rick Cook’s point about
additional heat from the sterling bezel is important and probably
did contribute to loosing one stone, but one stone was destroyed on
wheel #6 with water so I would presume that would indicate it was
more friction than heat.

Like any good car wreck, you have to get back in the drivers seat
and keep moving forward. I cut and polished two new stones from a
different slab, epoxyed them in, gave them a kiss with zam and a
fluffy buff and delivered the piece. It was probably one of those
failures that happened because the piece looked so much more
interesting with the new stones. Perhaps I look better with the
additional white hair that sprouted in the process. The piece far
exceeded the customer’s expectations and to see that delight is what
makes our world go round.

So, in the future when a customer wants a Malachite piece, I’ll take
this potential problem in consideration during the design process
AND… I’ll give the Malachite a good hard run before I cut and
polish it.

#9

Right on Rick. Overall I’ve had the same experience.

Cheers from Don in SOFL.