I've read the following. But, so far have not tested their
authenticity:-
1. When you place a real diamond on your eyelids it feels cool and
does not get warmer soon. While this is not so in case of a ordinary
stone.
2. Real diamond does not loose its shine on wearing it.
3. Real diamond is dense, when you take another stone of the same size
you will feel the real diamond heavier.
4. The best method, scratch a diamond with something, if a scratch
appears easily, it cannot be a diamond.

However, with that said, hardness of diamond is indeed one of it's most unique
properties, and it's behind much of what you can simply see with your eye when
you examine a diamond.  And THAT is by far, the best method to identify a
diamond.  Simple observation by a knowledgeable person, with a good magnifier is
the quickest, and most useful test.  

What you see, when carefully observed:

Diamond, because of it's high hardness, and the unique methods and equipment
used to facet it, has facets that are flatter, and sharper edged than other
stones.  Facet edges viewed through the stone are a crisp clear transition from
one facet to another, with no "line" in between.  That line, the slight rounding
over of facet edges seen on softer stones, is sometimes avoided mostly with the
best cutting quality of a few other stones, but most of the time, stones other
than diamond will show that "line".  If it's not there, look for other clues,
but if those edges between facets are rounded at all, it's not likely to be a
diaond.

Diamond is singly refractive.  Viewed through the stone, facets and edges on the
far side show no trace of double images or fuzziness caused by double refraction
in many other stones.  Moissonite, for example, is extremely double refractive,
and sapphire is enough so that you see at least a little image doubling.  the
test does not eliminate singly refractive stones like YAG or other garnets,
spinel, glass, or cubic zirconia.

The degree to which diamond is dispersive of white light into it's spectral
colors is quite distinctive.  Most other gems do it less, such as YAG, glass,
sapphire, or many others.  Some few simulants do it more, such as Cubic
Zirconia, which can be distinctively seperated from diamond by it's considerably
higher dispersion.

The way many round diamonds are shaped often leaves them with multiple
microscopic tiny fractures at the girdle.  Called girdle bearding, it's not
always there, but when visible, it's quite diagnostic of diamond.  Other gems
don't show this.  On diamonds where the girdle is facetted or polished, this
often is removed, but then you can see the crisp hard edges of the diamond at
the girdle, while almost any other gem with a polished girdle will have that
polished girdle edge be rounded over a bit.

The nature of the usual inclusions in diamonds are quite distinctive.  Not
unique to diamond of course, and better quality diamonds may not have inclusions
that are distinctive,  but the various synthetics, at least, don't have them.
And many other stones have types of inclusions that do NOT occur in diamonds

If you're still not certain, then the best next step would be to switch from a
simple loupe to a microscope if available.  Higher magnification will show you
more than the loupe.  or switch to one of those thermal diamond testers.  Good
quality ones are accurate, not all that expensive, and seperate all but a very
few materials.  and those materials which can fool those testers, like
moissonite with some of the testers, are easily seperated with the loupe in the
first place.  Frankly, with a good loupe and practice, (and for added ease in
observation, also add to your kit a small penlight flashlight), you will almost
never need anything other than the loupe to identify diamond.   For other gems
though, you'll soon find the need for a bit more equipment, such as a
polariscope or refractometer.  But even then, a good loupe should always be the
first identification tool you use.  Often, it's all you need.

Diamond has the same refractive index as air.

Look into it and the facet edges at the back are single lines,  that's
one of the reasons why you carry a loupe.

After that find one of these:

http://www.quicktest.co.uk/acatalog/Moissanite__and_Diamond___Moissan...

And make sure you know how to work it.

--
William Black

"Any number under six"

One thing to also note, which is generally different with diamond, is that
because of it's hardness, the facet edges are unusually crisp and sharp, so
looking into a diamond, the facet edges at the back are not only single lines,
but there is almost no line at all.  Just a sharp transition between one facet
and the next.  With softer stones, where the edge is almost always at least a
little rounded over by the polishing process, you actually do see a bit of a
bright line at the edge itself, since the edge has just a little width which
reflects light differently from the two adjoining facets.  With harder stones
and a better polish, (moissonite, again, is a prime example of this)  this can
be very subtle, but it's almost always visible if you look, especially with
higher magnifications, which might need a microscope.

And there are other visible characteristics too.  Girdle bearding, the crisp
flat facets, including the girdle if facetted, distinctive inclusions, the look
of either cleavage breaks or the splintery fracture surfaces of tiny chips if
present, the distinctive look of naturals, trigons, or other such remants of the
original crystal, the degree of dispersion relative to other gems,  the degree
of light return in well cut stones or other visible evidence of the refractive
index, and more.

You're correct of course, that a good loupe is the first and most important
diamond identification tool.

The electronic diamond testers, thermal probes, as you note, are also a good
second line of defense for those not as comfortable just using the loupe or for
smaller questionable set stones where you might just not be totally sure.  I
would suggest that the type of tester designed to specifically not return a
positive result with moissonite, which is high enough in thermal conductivity to
fool some of the cheaper thermal probes, probably isn't needed.  The reason is
that moissonite is the only such gem that not only doies resemble diamond but
that does fool the other probes, and moissonite is very easy to identify with
just the loupe, both due to it's faint greenish body color, and more
importantly, it's extremely strong double refraction, which shows facet
doubling, as you note above, as strong as any gem out there.  As strong as
zircons or peridots.  Makes them look distinctly fuzzy, sometimes even to the
naked eye, when viewed at an angle to the table rather than rights square on to
the table.

I'm no expert on gemstones,  I just know enough not to get caught,
mainly by buying only from reputable sources.

Although I made some money over the years buy buying large bags of what
everyone thought were imitation pearls at auction...

As an aside...

My wife acquired a diamond pendant recently in India as a gift, and it
came with a certificate identifying the source of the diamonds as
legitimate.

That's something I certainly haven't yet seen in the UK.

As all the 'blood diamond' stories are busy fading away as law and order
comes back to West Africa, and the diamond syndicate moves back in and
establishes its monopoly, I somehow doubt we ever will...

--
William Black

"Any number under six"

Also, it's perhaps no longer totally accurate to assume the diamond syndicate
has a total monopoly.  There are large portions of the diamond trade that bypass
deBeers these days.  They are still the largest player on the block, but
increasingly, there are other, paralell routes for diamond distribution, sold by
local authorities directly to the cutting industry, or those where diamonds end
up being cut locally to their origins.  Either way, the diamonds end up
distributed directly to the diamond wholesale trade, bypassing the whole
contgrol over distribution to the cutters side of things that traditionally was
the mainstay of DeBeers control.  For most of these channels, however, it is in
the interest of whomever is handling the stones, not to undercut the market
levels established by DeBeers, so these side channels don't disrupt the DeBeers
market plans as much as might otherwise be the case.  But the future seems writ
that DeBeers won't forever control the market, which is why that company has
been moving increasingly towards things like it's own Brand name on the stones
it handles, trying to establish a public demand for it's brand over others.
Potential future production of synthetic diamonds is another of the pressures
that is influencing these trends.

English provincial auction houses are a real gold mine if you know about
stuff they don't.

They're terrific on paintings, china, furniture and gold.

Less good on musical instruments, sculpture, scientific instruments and
tools.

As a general rule what they're selling is what's left over after someone
dies.

But I didn't really care,  I got about 20 strings for ?330 plus
commission (about ?335 altogether) so I was going to make money whatever
...

--
William Black

"Any number under six"

The whole thing with certificates in the showcase for customers is a pure
marketing decision by the retailer who no doubt thinks the notice will improve
sales.  

To a degree, the presence or lack of such notices reflects on the public's
confidence in the quality of their jeweler's wares.  In the UK, I doubt you'd
often see notices in the showcase next to the gold jewelry guaranteeing that the
items are up to standard, since the laws and processes there for hallmarking are
so traditional and strong that the average consumer already trusts it.  A notice
to that effect would elicit a response of "of course", rather than "oh, now I
feel reassured, trust it more, and am more likely to buy...".  With that
background of general trust in the jewelery's quality enjoyed in the UK, similar
notices of legitimacy of diamond sourcing might simply not be worth the trouble.
Does that sound about right?

Oh,  there's a legal requirement to display what's know as a 'Hallmark
display card' if you sell hallmarked products.

You have to buy an official one,  you can't just get a photocopy and
hang it in your shop...

http://www.hswalsh.com/Hallmark_Display_.aspx?i=TB170100&c=741

--
William Black

"Any number under six"

- An accurate scale
- Leveridge gauge with book, http://tinyurl.com/y9v5a26
- A refractometer, with appropriate light source, http://tinyurl.com/yd8xskq

And for your information, the following diamond simulants all have
higher specific gravities than diamond:
sapphire (this includes white sapphire) 3.96 - 4.25
spinel (this includes white spinel) 3.58 - 4.06
zircon 4.60 - 4.70
diamond 3.52

In closing I would like to say, that I am beginning to grow tired of
your inane postings.

You are correct, Ganesh, that hardness tests were once used, mostly by people
who had no other means to test anything, nor any gemological or mineralogical
knowlege with which to work.  Citing an historical precedent for a test which is
essentially based on ignorance should not suggest that it's still a valid test.

Not only can diamond be damaged, if not scratched, by softer stones, but in
testing, you can also damage the testing material.   And if you don't know how
to do it precisely and properly, you can get a false test result.  If, as you
suggest in your other post, it's a non valuable piece you test with and which is
harmed, then perhaps little harm is done.

 But even that can be deceptive.  A store I once worked for had a customer come
in and look at a gents diamond ring.  He liked the price, but thought it low,
since he'd been comparing at the very costly mall stores that marked things up a
lot in order to be able to routinely put them on sale...   So he wondered if the
diamonds were indeed real.  He asked.  But before waiting for an answer, he
figured he could find out himself, and dragged the ring across the glass top of
the showcase.  Sure enough, he had his answer, and happily declared that they
must be diamonds.  He was not, however, pleased when the store manager informed
him that the showcase glass top, which now had a severe and obvious swirling
scratch (he'd been quite vigorous in his "test", would have to be replaced, and
that it happend to be about a $250 dollar piece of glass.  How, he was asked,
would he like to pay for the damage his ignorance had caused...  And if you take
a fine old Tiffany's silver and rhinestone costume jewelry piece, and proceed to
scratch the rhinestones to make sure they aren't diamond, you're going to have a
very unhappy owner of that valuable piece of costume jewelry.

Here's the point, Ganesh.  To be blunt, you don't really know what you're doing
with diamonds.  And while it's great to research the archaic histories, and old
traditional methods of cutting, polishing, testing, mining, or whatever, of
diamonds and gems, it is just plain stupid to then assume these must be still
valid methods unless your research into current and modern methods confirms this
to be the case.  In the case of hardness testing, Every major gemological
authority or contemporary book on the planet would tell you it's a poor idea,
almost never needed, and should be done only in the rarest of circumstances, and
then only with training in how to do it with the least risk and most accurate
result.

The test was indeed "introduced" to test for fakes or non diamonds.  But keep in
mind, this introduction was by people who simply knew no better, nor any other
method, and there certainly were fine methods available to anyone who'd trained
themselves as to the nature of diamonds.  The history does not defend it.  As to
other stones one might need to identify as not being diamond, there are of
course, the actual fakes, or simulants like cubic zirconia or YAG.  But then
there are natural stones like white sapphire, white spinel, white natural
zircon, or even sphene and a few others.  All these can have significant value.
Some may be quite rare and fine gems.  You certainly don't want to test their
hardness.  And what about some of the newer synthetics?  Moissanite is synthetic
silicon carbide.  it is softer than diamond, but not by a whole lot, and is
tougher and harder to break.  That's a recipe for an accident if you try to test
it with a diamond, even if it were not also quite costly.  Then there is a
process which coats a synthetic cubic zirconia with a thin chemical vapor
depostion layer of amorphous diamond.  That too is quite tough and might fool
your test, or if not, would mean damaging an expensive and attractive simulant.
Or, what about actual synthetic diamond?  That too, is something that needs to
be identified, but your hardness test is useless.

As has been stated before, you simply never need a hardness test.  A good loupe,
and the knowledge of how to use it, is all you need most of the time.  The key
is not the loupe.  It's the knowledge.  This, by the way, is also all you need
for rough uncut diamonds.  Diamond crystals are extremely distinctive,
especially in gem grades.  Very little else in mineralogy looks at all anything
like them.

And please.  be cautious about what you put in your Blog.  The world is full of
people who are easily fooled, and fully misinformed, just waiting for more wrong
information.  They are better served by intellegent, careful postings that
reflect proper research, not hype or myth or legend, unless those are the actual
point of the Blog.  From what I saw, that doesn't seem to be the case.

Hope that's of use.

There is a saying in the Talmud that comes to mind.  "Ten wise men
cannot answer what one fool can ask."

In India there is little or no respect for craft skills and craftsmen
are paid very little.

There aren't any schools where he will be able to pick up useful
professional level practical skills, except those run for ladies who
want a hobby.

This has advantages,  a plumber or an electrician costs about $10 a day,
  and disadvantages in that highly skilled craftsmen such as jewellers
(Karigars) are paid little and learn their skills sat at their father's
feet.

Now musical instrument makers and cabinet makers can set up as
self-employed,  their raw materials cost little there.  But an Indian
working in precious metals almost certainly can't afford the raw
materials and tools to set up by himself,  especially somewhere like
Mumbai (where I live when I'm in India) where rents are high and
commercial rents are astronomical.

Every respectable Indian lady has a jeweller,  but he sits in his shop
and designs things on his shop computer for his customers and employs
poorly paid craftsmen to make the stuff.

The idea that a respectable Indian jeweller would make his own items,
or even have the practical skills to make them after designing them
would sound slightly absurd in a society when the normal mode of speech
for a person talking about a piece of jewellery they have had made by
their jeweller is: 'I have made this pendant'.

The guy's got problems not of his making,  but, to be honest,  what he
actually needs to get out of India and into one of the big European or
US jewellery schools for a couple of years.

--
William Black

"Any number under six"

Because of a tax levied on gold entering India the bullion business
there can be a very murky business indeed.

The cost of turning gold into jewellery in India is trivial compared to
the cost of the raw materials

The designers I've met are all related to the chap who runs the bullion
business,  so they're 'family'.  Nepotism is respectable in India and
jewellery design is not terribly difficult if what people want is 'more
of the same but slightly different engraving please'.

Because the political system has always been a touch unstable people
want portable wealth and jewellery is one way of having that without
suspicion that you've got a sack of gold bars under the bed.

Just about every branch of every bank in India has a safe deposit vault
under it where the family's gold is stashed.

  The craftsmen are almost incidental in all this. They're just people
turning the family's wealth into something that can be displayed without
vulgarity.

It's all really a lot more complicated than that,  and there are lots of
social pressures involved.

Layered on top of that there are the factories making jewellery for
export who don't appear to be factories at all but seem to use 'home
workers' as their labour source.  They're all locked into exclusive
contracts with overseas companies and won't sell domestically.

Jewellery is big business in India,  but there aren't any big
manufacturers,  the shopkeepers make their own stuff in their own
workshops,  but very little of it is what you'd call 'exciting'.

--
William Black

"Any number under six"

It is very much as it always was.

There is some spectacular work being done and it displays marvellous
mechanical skills.

But it's all the bloody same...

--
William Black

"Any number under six"