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You Can't Know it All!


#1

Hey Chris! just put it into a ulrrasonic solution, if it’s true
coral it will turn flat and loose it’s sheen. If it’s something
like glass nothing will happen. Don’t you hate that when somebody
tries to tell you something that’s obviouly not!!

P.S. Turquoise will do the same.
C.I A.
Matt W.


#2
           and how he worked for a gem Lab! I don't know if
there is any Easy Test for Coral but I do know one thing . THIS
WAS GLASS . Coral being a plant does not have a perfect Glass
finish and i compared it to pieces I have in my collection and
when you tap on it with a ring it didn't sound like glass. In
closing since I would not 

I am not a gg or gia or any other group of letters and DON’T know
it all. 8^)

One of the things that I do know however is that coral is NOT a
plant. It is mineral matter deposited by small coral animals. Some
corals when polished take a high shine and can look like opaque
glass.

If you’ve been sold plant material as coral in the past, it’s
those past sellers who have been less than honest with you.

Chunk Kiesling


#3
  I called him after close examination of the piece and told him
I found the piece to be Glass and after collecting carved coral
for 10 years I was quite familiar with the look and feel. I
explained that the back had a glass shiney finish w/tiny pit
marks which came from air I guess in the mold. Even when I tapped
on it with my ring it gave off a completely Glass sound. He
appologized and told me to send it back for a complete refund as
he did not have a chance to check it before he mailed it out 

hi chris,

i’m not really up to snuff with my gemology, francois jones is
much more qualified to answer, but here goes: the separation of
coral from glass is fairly basic. injected glass may have an orange
peel surface (but so can coral) and swirling body color and perhaps
some bubbles inside. coral could have a degree of orange peel (from
the polyps that create it), but it could not ever have swirling
colors. the specific gravity of glass varies quite a bit but it
would most likely be greater than coral, which is relatively light.
magnification is the best test and will produce proof of glass or
coral. coral will have a visible grain that can appear straight,
slightly concentric, or noticeably concentric. glass will have
swirling colors, bubbles, and most likely a parting line form the
mold.

i’m don’t think that coral is classified as a plant. memory tells
me that coral is an excretia from tiny animal polyps, that live
inside the coral.

best regards,

geo fox


#4

Chris,

Coral should not be too difficult for any qualified gemmologist to
identify. It has very characteristic growth structure and being
composed of calcium carbonate the easiest, however slightly
destructive way to test, is to put a small spot of dilute acid on
it. IT WILL EFFERVESCE. You still have to be careful though, as
some imitations may also be composed of calcium carbonate! Glass
will easily be differentiated by this method though.

regards - Nick
Bahrain


#5

glass also chips concoidally, chip some glass and see. i spose you
dont want to chip something you might consider ‘evidence’ but its
been handy to know once or twice. Robb Mitchell


#6

Another less destructive test would be to test the stone for
hardness, calcium carbonate being softer than glass…

Lee


#7

Chris, et al, A commentary I made in the past (and have been chided
for) made reference to a Dealer selling “Coral” beads, that several
of us knew to be glass. He was, on the third day persuaded to
change the sign to “Glass Coral Beads”. What I am reading here is
very disturbing as it appears this may not have been an isolated
incident. What is even more so, is the attitude “don’t rock the
boat.” I am certain this post will also have an internal reaction.
Teresa


#8

Hi Nick: That is very helpful can you tell me exactly how quickly
you need to wipe off the acid after testing the coral, and how
damaging is it! I do test metal when buying in the shop and usually
have something ready when I am questionable about a piece to wipe
the acid quickly so I do not damage the customers item!

Carol also was nice to tell me the refractive index of coral so I
guess he didn’t have one or didn’t want to test it either. But the
good news is that he returned my money in full and I thanked him
sincerely! The uniform glass finish on the back with the tiny
uniform air bubbles was too convincing for me and I found no
veining which doesn’t mean too much as glass can be molded with
graining and this carving was too intricate not to see some
irregularities in the carving, sometimes we have to weight all the
facts!

Kind Regards
Sunny and Gorgeous in CT.
Chris
http://www.tace.com/glitters


#9

Chris,

The acid you use should be applied in an inconspicuous place and
in as small an area as possible. It is preferable to do all of
this whilst looking at the piece under a microscope. The reaction
will usually be very fast if whatever you are using this method on
is composed of a carbonate. However, some carbonates are a little
more stubborn and if you think that what you are testing is a
carbonate, but it does not react as you expect, trying warming the
acid as this can make all the difference. The damage, if done in
this way will be minimal, in fact probably only the removal of the
polish will be the evidence left, i.e. a dull area, but this can
easily be repolished and the piece will look as good as before you
started. Like any new experience, it is a good idea to practice on
any pieces you have of little value to experiment and observe the
reaction/result. In MHO if you have or can get hold of any pieces
of broken: coral, malachite, azurite, magnesite, rhodochrosite,
calcite, pearl, M.O.P., limestone or marble etc… to practice
with, it would be best. The acids do not need to be concentrated
(these work too fast and are more dangerous to work with) so
dilute hydrochloric for instance is fine. Any acid should work
though.

Hope this is of help, but remember to be careful of yourself and
the item and only use the method (or any destructive test) if you
really think you must.

all the best - Nick
(Bahrain)