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Valid Tests for Jewelry


#1

Further to my ORCHID post Peter Rowe wrote to me offline. I thought
his explanations, reproduced below, should be very useful for ORCHID
readers and sought Peter�s permission to post them.

My point is that valid scientific tests are of course important in
any field. But just as important is the knowledge of tests that may
appear scientific but really are not. And this should help the
knowledgeable avoid some vendors who otherwise catch the uninformed
public as the current discussions on turquoise, pearls and some other
gems illustrate.

That said my mischievous mind wonders if the tables can be turned on
the not so scrupulous vendors. If your suspicion is roused shine a
laser pointer beam into a piece of jewelry and appear as if you know
what (test results) you are looking for. Watch if that person
squirms. He/she would if he/she knows that the piece being sold
isn�t what it claims to be. But you haven�t really said anything at
all!

   I do not work on and know very little about jewelry.  But I am a
gadgets guy.  Would a hand held battery powered flashlight sized
device- with a UV light source, a laser light*, a halogen light
source to shine through the gem and a nested bank of light filters
for colour, polarized light, a diffraction grating and possibly some
things I haven't thought of - be a useful tool for a preliminary
test of authenticity.  This should eliminate the obvious synthetics
or imitations.  For the more expensive gems tests by a certified
gemnologist would be prudent. 

Such devices are, sorta, made. The laser isn’t useful for much.
what’s useful is a simple penlight. Best are not the costly
maglights, but the real cheap ones with a simple tungston bulb where
the end of the bulb is a blob of glass, making it a strongly
condesing lens. These are great illumination sources to allow you,
with a loupe, to seem inclusions on gems much more easily than with
most other sources. Even useful under a gemological microscope
sometimes. The costly equipment version is a powerful halogen light
shining into a fiber optics light pipe with a condsing lens on the
end. Main advantage is that the battery doesn’t burn out, it’s a bit
brighter, and it earn much more money for equipment manufacturers
than do penlights (grin). The other items you mentioned, polarizers
and filters, are standard gemological instruments. They can be the
costly manufactured versions, or you can make your own. Polariscopes
are, after all, just two crossed polarizers. They tell you much about
the type of crystal structure you’ve got, such as glass vs. single
refractive cubic crystal material or doulbe refractive materials in
other crystal systems. And they can show you pleochroism, the
different colors some gems show along different optical axis
directions. They are less useful, though, in detecting synthetics
where the synthetic is the same material, only man made, from the
natural. For these, most of even the sophisticated gemological tests
amount to just careful observation under magnification. With that
penlight, you often can see what you need with just a loupe. If not,
then you need a good microscope. With some colored stones,
identifications between certain similar appearing stones (like
between aquamarine and blue topaz, or emerald vs. other green stones,
or jade vs. dyed jade) can be made with simple optical filters
emphasizing certain wavelengths. There are several manufacturers of
such simple filters, usually mounted like 35 mm slides. Not too
expensive. The costly gemological lab variant is a proper
spectroscope, which is much more versatile, but as I said, also more
costly. Defraction gratings can make a good spectroscope, but you
need the whole optical system, not just a bit of the grating. Still,
it’s just a slit, the grating, and a lens. You could, if you know
what you’re doing, build it. I’ve got one, which sells for about 60
bucks, that’s the about half the size of a cigarette. Works just
fine for what it does. Not as bright or as good as a larger prism
scope, and has no wavelength scale in it, but still fine for travel.
GIA sells it as part of their pocket lab setup, which includes a
polariscope, loupe, refractometer, spectroscope, and a couple
filters. Small case, fits in a coat pocket. The other item you
mention, UV light, is a useful tool for several synthetics, notably
the new diamond synthetics, dyed jads and dyed emeralds, and some
synthetic rubies vs the naturals. Other stones too, but not always
diagnostic proof.

For the newest synthetic diamonds, which are still in only limited
supply, add a good strong (really strong.) magnet. But the plain old
loupe is still perhaps you’re best all around identification tool.
With that, your penlight, and knowledge, you can be pretty sure about
most of the gem identifications you’ll come across.

The red laser pointer, by the way, although it looks like it OUGHT to
be useful, doesn’t turn out to be very useful. It’s just
monochromatic red light, after all. Your penlight is better at
showing up inclusions. And that nice pattern of little refracted
dots you see when it shines into a diamond is not due to the identity
as diamond, but simply to the precision of the facetting plus the
fact that it’s a single refractive gem. other single refractive gems
will, if carefully enough cut, do the same. There is one instrument
out there designed to shine a laser into a gem and photograph the
pattern of dots. Unless the gem is recut, that pattern can serve as
a fingerprint, positively identifying that particular gem, so it can
be verified if stolen and recovered. But it’s not anything special
to identify a gem from a synthetic gem.

   I did some quick tests.  A real diamond reflects the laser beam
as  multiple focussed points of light, very much like that of the
nightclub mirror ball.  Crystal glass lets most of the beam through
with some dispersion and attenuation. 

But you can visually tell it’s glass with much less effort. Just a
quick look with your loupe, and sometimes just the naked eye, is
enough.

   Jade lets through the laser, a dark green portion more easily
with less dispersion than the lighter  portions. On another piece
of jade the whole piece (a flat ring)  the  light scatters evenly
throughout the stone, letting little through. 

Again, interesting, but not particularly diagnostic, since it doesn’t
differ from other gems that look the same. For example, chrysoprase
will look about the same, and jade itself will vary a great deal from
one piece to another. But either density or refractive index will
show it. And your UV or a chelsea filter (cost about 20 bucks) will
detect dye in many cases.

   With UV light, stuff that gave a positive were microscopic
inclusions  in jade, the jade itself nothing.  

In SOME, but not all, dyed jade, the dye will glow faint dark red
when exposed to UV. Long wave especially.

  Tiny rubies on a necklace glowed  red while similar "rubies" in a
Siamese Princess ring remained dark. 

rubies are fun with UV. The flame fusion synthetics light up like
stop lights, stronger than any natural ruby. Not absolute proof of
that type of synthetic, but almost so. Natural rubies vary from
fairly strong fluorescence to almost none, depending on the amount of
iron in the stuff. This varies a good deal from stone to stone, but
especially with some locations from others, so fluorescence, while
not proof, is often used as an indication of the area of origin.

With sapphires, most natural ones are inert or almost so. But some
of the synthetics glow a chalky light blue.

   The black opal glowed blue as did animal ivory and horn. 

varies from stone to stone. Most ivory fluoresces, but the color can
vary some. Note that some of the things that simulate it also
fluoresce the same, so it’s not diagnostic.

It will be really helpful if there is a simple instrument that such
persons can use to make the most elementary tests. 

The simplest, of course, is just a loupe, plus a trace of education.
No instrument, after all, tells you anything without knowing how to
use it, and showing someone to see what they’re looking at with glass
versus other gems takes just a few minutes. The more sophisticated
true sythetics (by that I mean the gem, with the same chemical,
crystaline, and physical characteristeds as the natural, except that
it’s been made in the lab, which may leave teltale evidence as
different growth habits, inclusions not found in the natural, or
other suce evidence…) take more complex expertise and tests. For
these, there often is no simple test, since determining some of the
synthetics from their natural counterparts happens to be some of the
modst difficult testings in gemological practice. But the simple
determinations are easy. A polariscope can be made from a broken
pair of polarizing sun glasses, and will work just fine. It will
show you glass in an instant.

This is off topic but I hope our moderator will let it through. It
is on street vendor ingenuity. And you thought you had heard
everything.

As a kid I loved to go to Chinatown in the cool evenings because that
was where the action was and some of the best actions were itinerant
Chinese street vendors.

  1. This one sold Old Chinese Secret - Kidney Pills.

Us kids clustered like moths as soon as he pumped up the kerosene
pressure lamp and did his magic with the limelight mantle. The props
with their colourful carnival drawings and Chinese characters were
soon set up on the sidewalk. A kungfu assistant bangs on the gong
while they, including the cute daughter, do their martial arts dance
routine. After about ten minutes a crowd four deep gathers and he
starts his spiel. The master makes his pitch, his assistant
finishes the sentences with a flourish and the girl passes out the
pamphlets or hopefully some wrapped Chinese sweets for us kids.

Our attention captured he pulled out a couple of marked bottled
containing yellowish liquids - urine from a healthy kidney and
urine from two types of kidney diseases. How does he know? He went
on to pour a reagent into the �healthy� urine. The solution remained
clear. Pouring a reagent into the �diseased� urine turned the
solution black. The next bad urine sample turned blood red.

He then proceeded to crack open one of his kidney pills from a sealed
in a hollow wax ball*, dissolved that with water and then poured the
solution into the three urine test samples. Lo and behold the both
coloured solutions turned clear, showing how effective his pills
were to clear poisons in the kidneys. The good urine sample
remained clear of course. Needless to say he did land office
business. *(that�s how Chinese medicines were and are traditionally
packed before gel capsules were invented.)

I happened to be doing high school chemistry then to recognize that
what we had seen was the potassium ferricynide and the pot.
ferrocynide lab tests for the Fe+2 and Fe+3 ions. John Burgess will
have to help me out here as I no longer remember my chemistry but I
am quite sure he can duplicate the results described above. Likely
none of the (toxic) chemicals he used for the demo would be found in
his pills but for a guy who probably had never gone to science class
his inventive use of lab reagents for a carnival trick impressed me
to this day.

  1. Two guys were selling a new super liquid soap.

To demonstrate their liquid soap�s super cleansing powers they
soaked rags with very dirty black used motor oil which even had a
few soft crud inclusions. And sure enough; a squirt of their soap
into a basin full of water, a few swirls of the oil soaked rag into
that solution and the oil floated off.

The soap and the soap bubbles looked ordinary and I knew a bit about
soap-detergent chemistry to doubt their claims. Something about way
the oil from separated the rag when washed bugged me. My curiosity
wouldn�t let go for a whole week and then it came. That dirty oil
was squid ink. You can get lots of that stuff from the fresh fish
market � there was no such thing as frozen seafood in my time.
Clever - the vendors that is.

Kelvin Mok