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Gemstones are
a huge subject, so I will present you with a few
facts here that I hope will both help you to identify
with the subject and maybe sharpen your appetite
to look for more information.
There are some very good, readable books on the
subject of gemstones and if you are thinking of
buying a fairly expensive stone then I would encourage
you to do a little reading before buying. |
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 Learn
how to assess a gemstone’s value |
| Clarity
or Transparency |
| The
Cut |
| The
Colour |
| Carat
Weight |
| Fake
Gemstones |
| Imitation
Stones |
| Composite
Stones |
| Synthetic
Stones |
| Treatments |
| Star
Rubies and Star Sapphires |
| Fake
Star Stones |
| Diamonds |
| Emeralds |
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| LEARN
HOW TO ASSESS A GEMTSONE'S VALUE: |
When jewellers talk about the quality
of a stone, and precious stones in particular (being mainly
diamonds, sapphires, rubies and emeralds), they often use
four main criteria to make a value judgement. |
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These are Clarity, Cut, Colour, and
Carat weight of the stone in question. |
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| CLARITY
OR TRANSPARENCY: |
Clarity or transparency refers to both
the marks and blemishes on the surface of a stone and also
the inclusions (natural markings on the inside of gemstones)
that came about when the stone was created. |
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Generally speaking, the better the
clarity, and the fewer the marks on or in the stone, the
more valuable it is. However, a perfectly clear precious
gemstone can be treated with a little suspicion and if it
is expensive, it should be tested in a gems laboratory to
find out if it is natural. It costs me $15 to get a basic
report on an expensive stone by the Asian Institute of Gemmological
Sciences in Bangkok. This allows me to sell such stones
with confidence, and with a report. |
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A natural stone will very often have
some marks or inclusions which identify it as being natural
and genuine. Among the precious stones, inclusions come
in varying types and quantities associated with that type
of stone. For example Sapphires have fewer inclusions generally
than Rubies, and Rubies have far less inclusions than Emeralds. |
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Inclusions (natural markings on the
inside of gemstones) that are clearly visible to the eye
are very common in expensive emeralds, and form part of
their attraction. An emerald with no inclusions or marks
should be treated with a great deal of suspicion. |
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A very fine Ruby however may be virtually
clear of visible inclusions, and you can expect good Sapphires
to be mostly clear of such eye-visible natural markings. |
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However, the presence of marks and
inclusions do give the stone its own character and can be
proof of a natural birth. Do not be afraid to buy a stone
with inclusions; you should be more worried about one that
has none! If it is very clear, it may be a man-made synthetic
stone. |
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It is only when inclusions in a ‘precious
stone’ are very visible to the naked eye and really
detract from its appearance that you may consider whether
that is the right stone for you. Sometimes a smaller but
clearer stone (maybe costing the same or a little more)
is the better option. |
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Inspecting stones with a ten power
loupe, or magnifying lens, is the ideal way to check the
clarity. |
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Clarity is more delightful to the eye
than even good colour. |
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If a stone is opaque and has surface
flaws (bad clarity), but has a good colour, it will not
be so pleasing as a clear stone with a less desirable colour. |
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| THE
CUT: |
The cut of a stone is a demonstration
of the cutters skill at bringing out the brilliance of the
stone from the rough. |
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If making money is the main aim of
the cutter he will make the face of the stone as big as
possible at the expense of the correct proportions required
for brilliance and ‘life’ in the stone. |
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So the meaning of ‘cut’
here is creating the correct proportions of the various
parts of the stone to give ‘life’ to it. For
example, the refractive index of a Sapphire requires that
the depth of the stone, from top to bottom, should be 60
– 80% of the diameter. |
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This means that if it is cut with the
correct number of facets, the light will all reflect back
up to the observer so you should not be able to see right
through the stone, and read newsprint for example. If you
can see through it, this is called ‘windowing’.
This kind of defect in cutting will drastically affect the
price even if the colour and clarity are good. |
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Be aware that if a stone is cut much
deeper than necessary, you will be paying for it by carat
weight, and this stone too was cut to maximise its selling
price. |
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| THE
COLOUR: |
The colour of precious stones is a
great determinant in their value. |
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Pale colours are generally considered
to be less valuable than medium to dark colours. |
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Another aspect to Colour is when there
is a presence of a brown or grey hue. |
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So if the blue sapphire you are looking
at has a discernable element of grey, or the ruby has an
obvious brown hue present, their value should be considerably
less than a stone with ‘pure’, ‘strong’,
‘saturated’, ‘intense’, ‘vivid’
colours. These are all acceptable words to describe this
high quality condition. |
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The optimum colour for rubies should
demonstrate a red hue, medium to medium dark colour and
no visible brown colour. |
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Blue sapphires are the most expensive and popular of the sapphire family. Blue sapphires come from the same mineral group as Rubies, and the family is called ‘Corundum’. Chemically speaking, ‘Corundum’ is Aluminium Oxide and the red colour of Rubies is created by the addition of Chromium, and the blue colour of Blue sapphires is created by Iron and Titanium. Other colours, or ‘Fancy sapphires’, are created by a combination of these chemicals. |
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The most prized blue sapphires are
medium to medium dark blue, which is hard to imagine without
a comparison. Look at as many blue sapphires as possible
to build up a ‘comparison chart’ in your memory. |
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If the stone is nearly black, it is
less valuable than a good strong visible blue under the
lighting conditions in which it will be worn. So if you
expect your lady or the wearer to carry the stone at evening
dinner parties for example, consider what the colour will
look like in low light conditions. I prefer a lighter colour
blue, cornflower blue maybe, for this reason. |
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All this is especially true where emeralds
are concerned. Valuable emeralds should not have visible
hues of brown or grey. Again, the best ones are claimed
to be intense dark green colours, but not blackish. |
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Emerald is a mixture of bluish green
and yellowish green colours, both of which may be visible
in different conditions. |
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| CARAT
WEIGHT: |
The effect of carat weight on the value
of precious stones is dramatic. |
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You would be forgiven for thinking
that a five carat good quality blue sapphire would be five
times the cost of a one carat similar quality stone. Sadly
this is not true. |
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The cost ‘per carat’ of
the 5 carat stone may be many times the ‘per carat’
cost of the smaller one. To find out the ‘per carat’
cost of the stone, divide the cost of the stone by the carat
weight. |
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Gemstones are priced ‘per carat’,
and the prices are directly to do with supply. Simply, the
larger stones are much rarer and so the ‘per carat’
price is much higher. |
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The specific gravity of the stone has
an interesting effect here. Emerald has a lesser specific
gravity than rubies, sapphires and diamonds, and consequently
a one carat emerald may look twice the size of the others.
This may sound like a good reason to buy emeralds, but the
quality of emeralds is so variable that good quality stones
are still very expensive, even if they are small. |
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Look at any stone to see where the
weight has been put in the cutting. If it is very deep cut,
you will be paying for a lot of stone that you will not
be looking at. |
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But bear in mind the ‘correct’
proportions mentioned above in ‘Cutting’ and
the relative ‘life’ or ‘brilliance’
of the stone in question. Look and see if it is a very ‘shallow’
cut so that all the weight is in the front, or table. This
will make the stone look very big for its weight, but how
much windowing is there as a result and is there a lack
of ‘life’ and ‘brilliance’? |
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The distribution of the weight is therefore
also critical to the value of a stone. |
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Incidentally, in choosing the size
of a stone for a ring, consider the size of the finger,
be it for a man or lady. The stone needs to look good on
the finger and should be of the correct proportion. |
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For example, a stone that is too small
on a mans finger may look odd. And a stone that is way too
big on a ladies finger may look equally out of proportion. |
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Where a budget is involved, a small
fiery stone may be a better choice than a large dull one. |
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| FAKE
GEMSTONES: |
The meaning of fake here is gemstones
that are sold as natural, when in fact they are imitation
stones or man made synthetic stones, also undisclosed, unapproved
treatments, and also composite stones. |
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The key here is if they are fraudulently
sold as being a precious stone, and their real origin is
undisclosed. All these are legal if there is proper and
full disclosure when they are sold. |
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A brief explanation of each type follows: |
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| IMITATION
STONES: |
Imitation stones are those created
to look like what they are being sold as, but are not real. |
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For example, red glass as ruby, or
colour varnished quartz. These are often used in antique
jewellery, with maybe only one or two fake stones in a piece
containing many stones. Often these are foil backed or made
in a closed back setting. They may also have a coloured varnish or other coating on
the back. |
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Natural stones are always set with
an open back or with the pavilion (back of the stone) showing. |
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| Good indications of a suspect stone are: |
The price: is it being sold way too
cheap? |
Is it completely clear of marks or
inclusions? |
Look closely at the stone; does it
look like glass with rounded facet edges instead of crisply
cut ones? |
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Consider getting a lab report if you
are in any doubt about a valuable stone. |
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| COMPOSITE
STONES: |
Composite stones are stones made up
of layers of less expensive material glued together to look
like the real thing. |
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Composite stones are either DOUBLETS,
with 2 layers of stone or TRIPLETS, with 3 layers. It can
be difficult to spot this type of stone. |
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But if you hold the stone under water
(in a glass) and look at it under magnification (as you
should at all stones) from the side, you may see a joining
line. Often the different layers may be visible, they may
also be clear or coloured. Coloured glues between the layers
have also been used to ‘improve’ the look of
the stone. |
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This type of fake can produce an exceptional
look-alike at a small cost of stone, where labour is cheap. |
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Labour is cheap where most gemstones
are mined. |
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| SYNTHETIC
STONES: |
Synthetic stones are lab grown or man
made. |
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There is a huge market for synthetic
stones in the modern world, genuinely sold mainly under
generic names. |
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Emerald: There are two types of synthetic
emerald; hydrothermal and flux grown. These are both chemically
made in solutions and involve crystallization. |
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Sapphire: Synthetic sapphire has been
available since the early 20th Century, and is common in
all types of jewellery found today. |
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Flame fusion sapphire is made by melting
powdered chemicals and allowing them to crystallize. Melt
pulled sapphire is commonly used in industrial applications.
Flux grown sapphire is made by the same process as flux
grown emerald. Hydrothermal sapphires likewise are made
by the same method as hydrothermal emerald |
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Many flux and hydrothermal grown stones
are now produced in Russia and are widely sold as generic
creations. |
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| TREATMENTS: |
Heat treatment of stones is an accepted
practice in the trade because it leads to a permanent improvement
of the colour the stone, and it is too widespread to condemn
or stop. |
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Blue sapphires and rubies that have
not been heat treated are called ‘natural’ by
the trade and are now sold at a considerable premium. |
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Sapphires and rubies that are sold
as ‘natural’ or unheated from Myanmar (Burma),
Thailand or most Asian countries, including Australia are
also sold for greatly inflated prices ‘per carat’
because they are so rare. |
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These ‘natural’ stones
are already sufficiently ‘saturated’ with vivid
colour and the fact that they are not heat treated is an
additional rarity and value factor. |
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| STAR
RUBIES AND STAR SAPPHIRES: |
Star gemstones are getting more difficult
to find these days. |
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Star Rubies and Sapphires occur naturally
when ‘silk’ or ‘rutile needles’
(needle like crystals) are present in the make up of the
natural corundum. |
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The light reflecting off the cross
hatched crystals creates a six-rayed star which moves around
the face of the stone as you or the light source move around. |
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Naturally occurring stones are getting
rarer due to the pervasive habit of heat treating corundum
to ‘improve’ or deepen its colour and hence
its value. |
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Heat treatment of this nature is often
to above 1700 degrees Centigrade, and this dissolves the
crystalline rutile needles, thus destroying the chances
of a star stone. |
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Occasionally 12 rayed stars are found
and this is a result of a blend of mineral ingredients. |
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Star Rubies and Blue Star Sapphires
are the most well known and most sought after. |
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Black Star Sapphires have white rays
or gold rays and are mainly found in Thailand. |
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The majority of Indian star rubies
tend to be opaque and cracked on the surface, and are subsequently
cheaper. |
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The best stars are transparent or translucent,
which makes them much more valuable than opaque stones. |
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Star Rubies and Sapphires are highly
valued and considered ‘lucky’ stones all over
Asia. |
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Certainly you should expect to pay
quite a lot of money for a good example and the pleasure
of owning such a rare and beautiful stone. |
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| FAKE
STAR STONES: |
| The general features of a fake star stone are: |
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Profile: A flat base. |
Clarity: Opaque. |
| Star: A too perfect star with long
lines round the edge of the stone. |
Number of rays: Sapphire and ruby does
not have four rayed stars, only six or twelve rays. |
| Colour: A vivid red or vivid blue
colour stone. |
| Setting: The back of the stone is
closed to view. |
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If you come across a ruby or sapphire
star stone being sold with the above features, you should
be suspicious and request a report from a lab of your own
choosing, not the sellers. Better still, walk away! |
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| DIAMONDS: |
Diamonds have a set of descriptive
rules entirely to themselves, but it is enough to say that
they should be bought from a reputable source only. |
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There are cheap imitations of diamonds
as well as very good imitations that can fool professionals
sometimes. |
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Cubic Zirconia is a stone that may
be passed off as a diamond but it is fairly easy for a professional
to distinguish between it and diamond. Cubic Zirconia is
sold in its own right as a beautiful stone in less expensive
jewellery. |
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In terms of similarity to diamond,
man made Moissanite is so similar that a laboratory or special
tools are needed to tell the difference. Moissanite is sold
as the best man made copy of a natural diamond in existence,
and you should expect it to be considerably less expensive
than a natural diamond. |
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There are other similar looking stones,
such as white sapphire, which can be substituted for diamond,
so there are many reasons for dealing with traders you can
trust. |
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Throughout the genuine trade, these
diamond look-alikes are marketed openly under their generic
names. |
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The risk of fraud mainly exists when
someone tries to purchase stones away from a reliable supplier. |
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| EMERALDS: |
Emerald is a member of the Beryl mineral
family, and so is Aquamarine. In fact a blue/green Aquamarine
is considered by some to be a light green emerald. |
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Some of the most prized emeralds have
come from the Muzo mine in Colombia. Emerald is often described
as ‘grass green’, but that does not really do
justice to these fine stones. In early times they were kept
to refresh the eyes and the soul. Try to catch a look at
a good one and you can understand why. They are very desirable. |
Emeralds are not such a hard stone
as sapphires or rubies, rating about 7.5 on the Moh’s
hardness scale of 10. |
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Therefore care should be taken with
them, especially where emeralds are set in rings when they
are at risk of being knocked about. |
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An expensive emerald may be best worn
as a pendant or brooch. |
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Cleaning should be undertaken occasionally
by a jeweller as all emeralds are oiled to fill in their
natural minute cracks. |
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Cleaning at home
may remove the oil, and damage the appearance of the
emerald.
Treatment of emeralds with other fillers or coloured
oils should be disclosed by the seller. |
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