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Strange opal experience


#1

Dear all,

David, the gentleman I work with, has recently created a mounting
for a piece of dark opal. It is a very attractive piece of black
opal, and David assumed it was a piece he had sold the client, as
she has purchased several opals from us in the past. After further
checking, we find that she purchased it for about $200.00 on a
cruise. We would have estimated the value to be much higher, based
on visual observation. The stone weighs 1.02 carats. It has a dark
brown body color, with very good play of color- large, distinct
flashes of red and green.

Here is the weird part: when David got the stone wet during cleaning
of the finished piece, it turned very dark and lost its play of
color. We had the ring soaking in warm ultrasonic solution, though
the ultrasound was not running. The stone looked dark when we dried
it off, but then returned to its original appearance within
approximately 5 minutes. It also seems softer than regular opal,
with the finish being disturbed even with routine, careful polishing
of the metal around it. We have never seen or heard of anything like
this. Have any of you?

We hope you had a great holiday.

Take care and keep in touch.

Brenda
david lee jeweler
Golden Touch Jewelry
Mason City, Iowa


#2

Sounds like potch opal. We recently ‘treated’ a large piece here in
shop. Simply place in a super saturated sugar solution for a couple
of weeks at 20 Deg. C or higher and then pop into a bath of conc.
Sulphuric. The sugar is carborised and turns black high-lighting the
the opalescence. A lot of Australian boulder opal in the rough has an
opalescent sandstone backing. If the colour is strong you can make a
reasonably saleable rock from it by the above means. It’s similar to
the way onyx is died traditionally.

Regards, Mac

P.S. Treated potch opal is cut , pre-polished then treated. The
final fine polish is done after treatment as the carborised layer is
generally only a few mm thick.


#3

David, it sounds like you have a piece of Indonesian opal. The opal
you have is one that has to be worked dry because, as you found, the
color disappears when wet, but will return when dry. When I was
still doing shows, there was a dealer who specialized in this opal.
We talked a lot about the opal and how it was worked. There is some
of the Indonesian opal that has exactly the opposite
characteristics. IE when dry, there is no color, but when fully
wet, the color appears. These are good for display but not much use
in jewelry. Both types have very good play of color, and some rival
the best of Lighting Ridge Blacks.

I have a piece of Nevada opal with the same characteristics. The
opal is prone to absorbing oils and chemicals, so cleaning with
water only is a must. As you found also, it is a very soft opal.
Care should be used in setting it, and if you attempt to re polish
it, I would recommend not using Cerium Oxide as it will acclimatize
in the porous opal and discolor it. Diamond on a fiber belt/disk
will give you the best results. When polishing a mounting, care
should be taken not to load the stone with rouge. I recommend using
a pink silicon wheel and polish just to the edge of the gold, not
onto the opal surface. This seems to work well.

I have no experience with the stability of the opal, but based on
it’s similar characteristics to some of the Nevada opal, it might
not be very stable. My dealer friend didn’t care to share this
I would be interested in hearing from others on this
point.

Don


#4

Brenda, Sounds like hydrophane opal. As I recall there was quite a
discussion of it on Orchid last year. A search of the archives
should give you all the info you want. Jerry in Kodiak


#5

Check out Hydrophane opal. That is what you have. I ran into this
animal unknowingly and it caused me much grief till I got it
identified and learned more about it. My inclination is not to use
it in any type of jewelry at all. My client had bought it on the web
from a company in Portugal. The material was misrepresented to my
client by the company. Live and learn.

Bill


#6
 Sounds like potch opal. 

Not potch, potch is clear transparent opal with little or no play of
colour. You mean opal matrix which is porous and “treatable”.

Not sure what sort of opal Brenda at David Lees was talking about.
I’m only familiar with the South Australian opals but as I’ve said
before, I would never put an opal in anything other than ordinary
water. Put an Australian opal in a soapy solution and you will lose
the play of colour sooner or later depending on the porosity of the
stone. That’s the nice thing about opals… you will rarely find two
the same. So treat them all with respect.

Cheers for now, Renate


#7
Not potch, potch is clear transparent opal with little or no play
of colour. 

Not so. Potch is common opal which has no fire or play of color.
It can be various colors and is more often opaque or translucent than
transparent. It can also be quite beautiful: The blue, opaque to
translucent opal from Peru is just one example of this.

Beth


#8
 Not potch, potch is clear transparent opal with little or no play
of colour. Not so.  Potch is common opal which has no fire or play
of color.  etc 

Now there was an “off the top of my head answer”. You are no doubt
right Beth. There are many wondrous things on (and in) this earth
that I have yet to learn about. I do have some lovely pieces of
"honey potch" though, which comes out of Andamooka which does have
fine green flecks of “play of colour” when looked at in the right
light. Definitely transparent too. Methinks there are many grades
between common and precious opal and lots of rocks that refuse to
fall into one category or the other.

Cheers, Renate