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Jade flaking and fracturing issue


#1

Recently I have been making cabochons from nephrite jade of various
sources with varying issues coming up. It would be great of hear the
experience of others.

I’ve cut Wyoming jade but don’t like the stuff.

I have gotten what I have come to understand as ‘utility grade’,
(stone used for sculpture rather than gemstones), Siberian slabs
that work up pretty well but have inconsistent inclusions and is
often milky and clouded.

Recently I acquired both Alaskan gem quality rough and Siberian gem
quality slab and rough from two different sources. The Alaskan works
up pretty well but is somewhat pale with low transparency.

As an ascetic choice I prefer the dark green color of Siberian gem
grade jade. But the slab and rough that I have gotten from two
sources flakes and fractures easily. It runs softer through the slab
saw than the Alaskan stone. And fractures appear in sawing with a
thin diamond blade under water. Rough shaping on the dopping stick
causes edge fracturing, both top to bottom chipping and fissures
into the stone appearing. Even starting with a 600-git Ameritool
diamond wheel.

Today I intend trying less pressure on the saw.

On the wheel I am wondering if the hard Ameritool disc could be the
problem. Do I need to work with something on a softer backing?

Any ideas or perspectives would be welcome.

I am reluctant to do much more work if it means destroying any more
rough stone rather than making some finished cabochons.

Thanks.
Pat Rogers


#2
But the slab and rough that I have gotten from two sources flakes
and fractures easily. It runs softer through the slab saw than the
Alaskan stone. And fractures appear in sawing with a thin diamond
blade under water. Rough shaping on the dopping stick causes edge
fracturing, both top to bottom chipping and fissures into the stone
appearing. Even starting with a 600-git Ameritool diamond wheel. 

Well, here we go again. I am beginning to think that gem dealers are
more creative with language than political consultants.

Jade is a trade name with encompasses, or better to say should
encompass nephrite and jadeite. Nephrite is tougher, but both stones
are very, very tough. Historically, pieces of jadeite were used as
anvils by ancient jewelers. Whatever you are using cannot possibly
be any of these minerals.

Leonid Surpin
www.studioarete.com


#3
But the slab and rough that I have gotten from two sources flakes
and fractures easily. It runs softer through the slab saw than the
Alaskan stone. And fractures appear in sawing with a thin diamond
blade under water. 

Pat, I never was a jade expert - maybe someone here is more so… I
got a piece of Wyoming black jade once that looked pretty good. When
I cut it I found that it was layered like shale or slate. IMO it WAS
jade, it just had this certain formation and grain to it. Same thing

  • cleavages, fractures, snowflakes - lots of problems. It wasn’t me
    or the equipment, it was that the rough was pretty much un-cuttable.
    Just a story, I don’t know if it applies to your issues or not.

#4

Its always hard with nephrite jade when making anything as well as
making cabs. There is a definite grain to it and the different
qualities, fractures, inclusions, colours, ect make it more
difficult. I have seen cab machines eatting up enough jade for 10
cabs before they come up witha useful one. The best nephrite jade
comes from here in New Zealand. I am a bias of course and it is hard
to get hold of if you dont know the right people. The colours are
endless, there are differing qualities of stone also. Since you are
working the cabs by hand makes for better results than with cab
machine. The diamond tools make for easier cutting and shaping but
definitely recommend finishing with sanding stones. So check the
grain out and go with, its hard though to get a good cab from some
of jade. good luckcheers

Neke


#5

I have cut cabs from nephrite from Wyoming, California, and British
Columbia, also jadeite from Burma and California. Most of the
nephrite was very uniform in texture and hardness, except for some
schistose nuggets from south of Big Sur. Nephrite is extremely tough,
so edge chipping, flaking, and fracturing should never be an issue in
good material. You should be able to rough out with 180 grit, sand
with 325 and 600. I use a resilient backing on my 325 to help get rid
of flats before going to 600. My polish of choice for nephrite has
always been chrome oxide on leather. Some of the best green color I
have seen in nephrite has been in Wyoming material, and the blackest
and most finely uniform nephrite with the best polish has been from
Wyoming, too, so it seems that your experience is very different.

Your description of the Siberian material suggests that it is not
pure nephrite, or perhaps it is structurally very foliated or
schistose so you experience the difference in apparent hardness.

Richard Davies
Cutter in Fairfax


#6

Once you understand what jade is doing, it is the easiest things in
the world to get a great polish on.

Jadeite is easy to polish, so I am going to talk about nephrite.
Most of my cutting is done with Wyoming jade.

nephrite is a dense structure of interlocking fibers, although I
have never actually measured this with a scanning electron
microscope, which would be proper, here is what I have observed:

when cutting with a saw, or grinding, these fibers to pull apart from
each other. although they stay in place, the “pulling apart” causes
loss of optical transmission continuity, aka subsurface damage, also
known as subsurface fractures.

in a faceted stone, this damage would be obvious and visible, as
cracks and flaws. in a piece of jade, the fractures are not so
obvious, but they are still there, and will make themselves known as
the stone will appear to not take a proper polish.

sanding, as opposed to grinding, removes the damaged portion of the
surface.

here is the important part: you can calculate the amount of
subsurface damage you are going to get. Again, I have not measured
this with an SEM, but the amount of damage appears to be about 1.5
times the grain size of the abrasive used to grind. So, if you grind
with an 80 grit wheel, which uses an abrasive of about 1/80 of an
inch or 0.0125", you are going to have damage of about 0.016- 0.019".
roughly equivalent to the thickness of a, what, 26 gauge piece of
metal?

when you grind on a 120 grit wheel, these numbers change

so, using the 80 grit example, during sanding you will need to
remove the 0.016" damaged surface, to get down to the undamaged
subsurface material that has optical continuity.

note: when you take a slab of jade off of your slab saw, the ENTIRE
surface of the slab has subsurface damage - so when you wet it to
see the color, all you are going to see is a dull, frosted subdued
color. you have to polish a test area to see what the jade is
actually going to look like. I have cut 100’s of pieces of jade -
every time that I am absolutely sure that I have a dud, I polish it -
2/3 of the time it really is yard rock, the rest of the time it is
some of the best material i have. So much for experience.

so, that is the theory, hope it helps

to see some examples of polished jade, please denvergemshow.com

Mark Zirinsky, Denver


#7

Some good responses. Thanks all.

John Donivan:

I didn’t like the appearance of the Wyoming jade at all. I got some
last year and while it worked readily and took a good polish it
didn’t have the character I want in jade.

The Canadian Nephrite jade I have has more black deposits and grey
patches. I am hoping that the supplier will provide more consistent
stone with better translucence in the future.

The same supplier provided the Siberian stone and has since admitted
that other workers have had the same problems handling the stone.
Its a shame because the color os wonderful and promises to produce a
beautiful cab. But shaping just keeps flaking.

leonid surpin:

The dealer I am currently buying from has an impeccable reputation.
Our conversations about the difficulties have been open and honest.

I suspect that he bought the Siberian supply from the same source I
originally bought from. I had concerns about his storage when I
visited his warehouse. So my suspicion is that this originating
supplier of Siberian stone is the problem.

It is also curious that the Siberian stone is much softer in the saw
and in grinding than any other jade I have worked with. Too bad.

The softness of the Siberian stone supply concerns me more as I
research and work with it. The fracturing is depressing but not
unheard of. The softness seems to make the fracturing worse.

Neke Moa:

You bring up an interesting point.

Grain. A new thought.

The piece of stone I am working with started about a foot long
tailing off from about 3-inches in diameter at the thick end to an
inch at the tail. My inclination has been to cut 1/4-in. slabs from
one end. These slabs have consistently experienced vertical flaking
and chipping around the edges as I shape the blanks.

At your instigation, I will attempt to cut a thicker slab and
produce my blanks from cross cuts of that. This should create a cross
section of the fracturing. Hopefully reducing it. A light hand on the
wheel may then better handle the fragility.

Thanks.
Pat Rogers


#8

Neke:

Your grain idea definitely improved things with the Siberian Jade.

The following is using a fast wet 260 diamond disc and handling the
stone by hand rather than dopping it from the start as I usually do.

Changing the axis of the slab cut, by 90 degrees, from what I had
been cutting certainly improved the grinding down for the blank.
Flaking stopped. But shallow vertical fissures are still appearing
around the edges as I work the blank. And after grinding on the
blank a new fissure line has become visible almost across the center
of the 1-inch oval stone. Although it has not fractured.

Better. But nothing I would try to show anyone.

I’ll work this stone just to see what happens but its not something
I can brag about.

I’ve a feeling that I will settle in using the Canadian stone since
it is more stable.

Thanks.
Pat


#9

Since Nephrite is an Aggregate of Actinolite and Tremolite, both
with perfect cleavage, it’s no surprise that Nephrite jade can
sometimes be lamilar. That’s one of the reasons it gets an “orange
peel” surface when cutting that turns some cutters away from dealing
with it. Another reason is that it can form with Serpentine. Much of
the Nephrite Jade from the northern part of western Washington State
is that way.

By definition, not all Nephrite is Nephrite “Jade”. I can’t tell you
what isn’t. A gemologist friend of mine saw a cinnamon and gray cab
of Nephrite from “The Equality State” in my collection and said “Is
that Wyoming Jade?”

Leonid, you said

Jade is a trade name with encompasses, or better to say should
encompass nephrite and jadeite. Nephrite is tougher, but both
stones are very, very tough. Historically, pieces of jadeite were
used as anvils by ancient jewelers. Whatever you are using cannot
possibly be any of these minerals. 

Are you saying this like you were saying that turquoise with matrix
isn’t turquoise and blue-green turquoise isn’t turquoise? Because,
knowing Nephrite as much as I do, (not much) I know that Nephrite
Jade has a cleavage plain that would be perfect if it was not an
aggregate. As it is, the cleavage plain is imperfect. I often slam
slabs on the edge of my anvil so they will break upon these natural
faults.

And I read nothing in the original post that seemed inconsistent
with bad Wyoming Jade. I, too, have some of it. The material I have
came from an area near Jeffrey City.

TL Goodwin
Lapidary/Metalsmith
http://thepacifikimagestore.com


#10

I have a chunk of jade that is also flaky…the interesting thing
is, it has chatoyant tendencies. Not sure where it is from. Does
yours have any chatoyance?

Jeanne


#11
And I read nothing in the original post that seemed inconsistent
with bad Wyoming Jade. I, too, have some of it. The material I
have came from an area near Jeffrey City. 

I think this will be a great spot to pay a homage to Shakespeare:

'Tis but thy name that is my enemy;
Thou art thyself, though not a Montague.
What's Montague? it is nor hand, nor foot,
Nor arm, nor face, nor any other part
Belonging to a man. O, be some other name!
What's in a name? that which we call a rose
By any other name would smell as sweet;
So Romeo would, were he not Romeo call'd,
Retain that dear perfection which he owes
Without that title. Romeo, doff thy name,
And for that name which is no part of thee
Take all myself.

When we use names like jade, diamond, any other gemstone we implying
that material described possesses gemstone properties: beauty,
durability, rareness. If any of the three is absent, it is just a rock
irrespective of anything else.

leonid surpin
www.studioarete.com


#12

The material from Guatamala (sp?) has some chatoyance. It also takes
a beautiful polish.

This thread has contained statements about jade /nephrite that are
very questionable in my experience.

KPK


#13
I suspect that he bought the Siberian supply from the same source
I originally bought from. I had concerns about his storage when I
visited his warehouse. So my suspicion is that this originating
supplier of Siberian stone is the problem. 

I am somewhat familiar with Siberian Nephrite. The best source is
Ospinskoye deposit. Nephrite is apple green, some with chatoyancy,
and no problems whatsoever.

leonid surpin
www.studioarete.com


#14

Jeanne,

I cannot comment about your specific ‘jade’ but I can tell you that
some nephrite jade from Taiwan has chatoyant qualities. While living
in Taiwan in the 70’s (thats the 1970’s) I was active in the Chinese
gem cutting community and had opportunity to see many unusual
materials. One was this chatoyant nephrite being mined in southern
Taiwan. I have several pieces of rough and a small bag of stones
that have beautiful ‘eyes’ in them.

Cheers and hopefully yours are not too ‘flaky’.
Don in SOFL.


#15

so far, it’s mostly the outer crusting that is flaking badly. My 10
inch saw has been acting up so I haven’t really cut into it much yet.

I was wondering if that structure is what causes the chatoyance
compared to other nephrite? Or is it an additional mineral that does
it? I have no idea where mine is from. yet another estate ebay parcel
I picked up because something caught about it.

Jeanne


#16

To All:

I have tried several new ideas from changing the axis of the slab
cut to using 400 and 600 grit wet sandpaper, by hand, after the
260-mesh diamond wheel. But the fracturing still happens with one
fracture threatening to chip while another can be seen with the naked
eye running the width of the side as well as being visible across
most of the back.

Sanding helped to reduce the shallower cracks on the sides but also
shows the depth of the lesions. I’ve a lot more reduction sanding to
bring the stone down to the level of the lesions.

All in all I am afraid that the stone is just not worth going
further since it continuously threatens to break further and
cabochons with cracks running into the stone will never be worth
showing.

I am awaiting some Canadian stone instead. Too bad. I love the color
of the Siberian stone but the work 100% waste is not worth the time.

Thanks for all of the ideas.
Pat Roger


#17

Pat…Didn’t give my additional 2c last week…been tied up with a
sick wifie but…when nephrite flakes like that, put it in the
garden or fish tank. I know of no treatment or process that will
overcome such flaking. I’ve cut lots of jade, both jadite and
nephrite and because of these experiences I rarely (if ever)
purchase jade without being able to look, touch and feel (sometimes
taste too). Hope you have a better experience in the next batch.

Cheers from Don in SOFL


#18

Re fractures and feathers in nephrite----When I learned to cut stones
over 50 years ago in the back of a local rock shop one of the things
we had lots of was B.C. nephrite----the owner taught me how to deal
with the vagaries of this sometimes difficult stone. one of the rules
was —never buy material that has been blasted — the fracturing
and feathering often is not evident until the fine sanding and
polishing stages. the nephrite may be one of the toughest stones but
the effect of blasting isto transmit tiny fractures throughout the
material because of its very fibrous origins. He would also determine
the best direction to cut slabs for best polish results by cutting a
small cube, marking all the faces relative to the large piece,
polishing all faces of the cube, and then orient the piece to saw
slabs with the best polishable surface on the face of the slab. this
was in the days before easily available diamond polishers of today.

Another trick was to mix the tin oxide with the strongest cider
vinegar he could find—apply on a leather disc and apply enough
pressure to get it HOT. Prior to this however you have to DRY sand
at 400 and 600 to a good sheen—the SHINE should come up very
quickly---- it still works for me after all these years and I have
cut jadeite and nephrite from all over the world my two
favorites are BC Cassiar nephrite—adark green base with bright
green flecks throughout and the old Clarks ebony black from Wyoming
(neither ajadeite or nephrite but sold as “jade”)

Dave Barclay
Gemmolgist/geologist/lapidary
C&D Gemcraft