diamonds, coloured gemstones, pearls and precious metals crg.pdf · about the jewellery we sell, it...
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CIBJO is the international trade organisation of
the world jewellery industry. Its members comprise
representatives of commercial organisations
and over 70 national jewellery associations in
more than 34 countries. Established in 1926,
CIBJO educates and communicates on matters
of business responsibility by raising awareness
of consumer confidence issues, distributing
information and acting as a forum for the
worldwide industry to debate its views.
CIBJO’s ‘Code of Ethics’ is designed to give its
members overarching principles to help them
operate according to strict ethical, business
and consumer confidence guidelines. Jewellery
retailers can refer to CIBJO’s membership to
identify whether their suppliers should adhere
to the Code.
CIBJO – The WOrld JeWellery COnfederaTIOn
www.cibjo.org
DIamOnDs, COlOurED GEmstOnEs, PEarls anD PrECIOus mEtalsa COnsumEr GuIDE
Welcomea piece of jewellery is one of most inspirational, exciting and magical purchases
you can ever make. Whether the piece is for you or a loved one this guide will
take you through the basic information about diamonds, coloured gemstones,
pearls and precious metals.
the guide has been put together by the most knowledgeable experts in the
global jewellery industry. We hope that by empowering you with the knowledge
about the jewellery we sell, it will help you make the right choice.
Please enjoy your guide to: Diamonds, Coloured Gemstones, Pearls and
Precious metals.
Best wishes
Jonathan Kendall, President, marketing and Education Commission, CIBJO
Contentslearn more about diamonds 2
Introducing gemstones 9
mini guide to birthstones 11
understanding pearls 14
Overview of precious metals 18
this guide was co-ordinated and produced by andré marais, Forevermark,
De Beers Family of Companies and roland naftule, CIBJO President sector III
the project Gem materials co-ordinator
learn more about diamondsDiamonds are one of nature’s most rare and
precious gifts. their age and history, symbolism
and amazing brilliance, make them the jewel
of all jewels.
this section of the guide gives you an
understanding of diamonds. It is designed to
help you appreciate their complex charms and
to give you more information and practical
advice. then you will have total confidence
in your own choice.
First discovered in India, diamonds are now
mined in many parts of the world, including
africa, australia, Canada and russia. they can be
found in remote deserts or even the ocean beds.
amazingly, only a tiny portion of those found are
of a size and quality that can be cut, polished
and set into jewellery.
Diamonds are symbols of love, devotion, pride,
wealth and power – the ultimate gift from a loved
one, or to yourself. the decision to buy a diamond
does not come lightly. It is therefore crucial you
know what you are looking for in your diamond.
there are at least 13 factors that affect polished
diamond value but the most important factors
when determining its quality are known as the
4 Cs. these are the diamond’s carat weight,
its cut, its colour and its clarity. the key thing
to note is that no one C is more significant than
another. a particular combination of the 4 Cs can
be chosen to suit a particular budget, occasion,
design or jewellery piece. Each diamond can
be described by its particular combination of
the 4 Cs, but its unique beauty is much more
than a list of characteristics. When you choose
a diamond to own or to give, it becomes special
– regardless of its place on the 4 Cs chart.
Importantly all diamonds are beautiful and come
with a heritage of being at least 900 million
years old.
2
emeraldassCher CushIOn hearT marquIse Pear rOundOvalPrInCess TrIllIanT
COmmOn CuTTIng sTyles
COlOur
as we talk about a diamond’s colour we can
talk about two different aspects. When most
people talk about a diamond’s colour they are
actually referring to colourless or near colourless
diamonds. Colourless or near colourless
diamonds remain the most available and the
most popular with consumers. However, what
most people are unaware of is that diamonds
are found in almost every colour. Diamonds
occur – albeit very rarely – in red, blue, green
and all other colours of the rainbow and are also
known as ‘fancy colours’. Due to their rarity they
can fetch exceptional prices.
there are more than 20 subtle grades of colour,
identified in alphabetical order from D-Z.
Variations are so slight that colours must be
graded by an expert under controlled lighting
conditions and compared against a master set for
accuracy. those at the upper end of the scale will
be more expensive, as they are rarer. However,
they are difficult to discern with the naked eye.
Top Tips
• When buying a diamond, consider the setting
and the metal, as it can be used to accentuate
or de-emphasise the colour.
• Be sure to try on the diamond jewellery as the
colour may look different when worn on the body.
• If purchasing a loose diamond, place the
diamond on the top of your hand and compare
it with a similar stone mounted in jewellery.
CaraT
Carat is often mistakenly used to refer to a
diamond’s size, but it is actually a measure of
weight. One carat (equivalent to 200 milligrams)
can be divided into 100 ‘points’. a 0.75 carat
diamond may also be described as a 75-point
or ¾ carat diamond. larger diamonds are found
less frequently in nature, so they can command
a significantly higher price. For instance, a one
carat diamond will cost more than two ½ carat
diamonds of equal colour, clarity and cut.
However, your diamond is not valued by carat
weight alone. two diamonds of equal carat weight
can have very different values, depending on
cut, clarity and colour. Furthermore, a smaller
but perfectly cut diamond of whiter colour and
flawless clarity can be more valuable than a larger
stone that is less white and with more inclusions.
Whatever its carat weight, you should choose
the diamond which suits you and your budget,
the occasion and the design you like best.
Top Tips
• a diamond can appear larger or smaller than
its actual weight, depending on its cut.
• look at different designs and mountings as
they can affect the appearance of the size
of diamond.
CuT
nature determines so much about a diamond,
but it takes a master cutter to reveal the stone’s
true brilliance, fire and ultimate beauty.
regardless of size or shape, a well cut diamond
will reflect light within itself, from one mirror-like
facet to another. to spot a well cut diamond,
you are looking for three important factors –
brilliance, dispersion and scintillation. Brilliance
is the return of white light to the viewer’s eyes
from the internal and external surfaces of a
diamond. Dispersion or as it is more commonly
known ‘fire’ are the flashes of spectral colours
that come from a diamond. scintillation is the
sparkle or flashes of light you see as the diamond
or light source moves. If a diamond is cut too
deep or too shallow, light will be lost through the
side or bottom; this reduces its brilliance and,
ultimately, its value.
the cut of a diamond can also affect its visual
size. two diamonds with the same carat weight
can appear to be different sizes depending on
the shallowness or shape of its cut.
the cut at its most basic level also refers to the
shape of a diamond and is a matter of personal
taste, with the round brilliant cut the most
popular. although there are many diamond
cuts the most well-known other shapes are the
asscher, cushion, emerald, heart, pear, marquise,
oval, princess and trilliant. You might also
hear of trademarked, copyrighted or ‘branded
cuts’ which have been developed by individual
companies. a branded cut will have something
unusual or a parameter that is different than
the standard cut. shapes other than round are
referred to as fancy shapes.
Top Tips
• When choosing a diamond, hold it up to
the light and see the fire. see how the light
dances around – it should throw out a
rainbow of colours and display the diamond’s
natural brilliance.
• ask your jeweller to show you all the cuts
and shapes.
• Be sure to try on a good selection to find
the perfect one for you.
2 CTs 1.5 CTs 1.25 CTs 1 CTs 0.75 CTs 0.50 CTs 0.25 CTs 0.10 CTs
75 points 50 points 25 points 10 points
guIde TO aPPrOxImaTe CaraT sIze
heIghT Of CrOWn
gIrdle
dePTh Of PavIlIOn
WIdTh Of TaBle
Well CuT TOO deeP TOO shallOW
3 4 5
ClarITy
the clarity of a diamond is its most obvious
characteristic as no two stones are alike.
Clarity characteristics include a wide range
of features but they are generally broken down
into two basic categories: blemishes, such as
surface features like scratches and nicks, and
inclusions, which are internal features and not
easily removed.
the professional will view the diamond at
10 x magnification in a controlled environment
and decide on the clarity grade considering
four characteristics of the blemish or inclusion:
size, nature, location and number. Obviously,
as a buyer you cannot see the detail of these
blemishes, but they can affect the overall
appearance of the diamond.
Flawless diamonds are the rarest and thus, most
expensive, but ultimately, small inclusions do not
affect the beauty or the brilliance of a diamond.
Be aware of the inclusions, but don’t let them
deter you from buying a diamond you love.
Top Tips
• View and try on all ranges of clarity. some
inclusions can be hidden by a mounting and
do not detract from the diamond’s beauty.
Compare them to see if they affect the
reflection of light – you will most likely find
them equally brilliant.
• If the diamond comes with a certificate, look
to see where and how many inclusions exist.
an examPle Of a CrysTal InClusIOn
an examPle Of a feaTher InClusIOn
6
synTheTICs
‘synthetic, laboratory-created and laboratory-
grown diamonds’ refers to diamonds
that are manufactured by man. they were
first made in the 1950s in industrial quality
and have been manufactured in commercial
jewellery quantities and qualities since
the 1990s.
TreaTmenTs
a diamond that has been altered by any process
other than cutting and polishing is considered
as treated. treatments may artificially modify
the colour and/or the clarity of a diamond.
Introducing gemstonesGemstones are much more precious than most people
realise. there are many different varieties and colours
and they are a fascinating group to explore and own.
they have magical qualities that have entranced and
excited generations for thousands of years.
While we cannot go into detail about each individual
gemstone we want to provide you with an overview
of the many and varied types available today.
most gems are natural, inorganic minerals. However,
some gem minerals, such as opals or natural glass are
amorphous and some gems are organic, meaning they
come from plants or animals, such as: amber, coral
and ivory.
to be called a ‘gem’ it must possess the following
features: beauty, rarity and relative durability.
When looking to buy a gemstone, these are the
three topics to quiz the retailer on.
9
Coloured gemstone section written by the Gemological Institute of america,
Carlsbad, California. all rights reserved.
Images for this section are courtesy of the Gemological Institute of america. Faceted gems
courtesy of the Dr. Eduard J. Gubelin Gem Collection, now part of the GIa Gem Collection.
mini guide to birthstonesa popular reason for giving jewellery with a
specific gemstone is that they can also be
a person’s birthstone. Below we outline which
stones are linked to which months of the year.Alexandrite and other
chrysoberyls
Amethyst
Aquamarine Other beryls Citrine Emerald The feldspar group
The garnet group
Jade Kunzite Lapis lazuli Opal
Organic gems Peridot Unusual quartzes and chalcedony
Ruby Sapphire Spinel Tanzanite Topaz Tourmaline Turquoise Zircon JANUARY
Garnet
FEBRUARY
Amethyst
MARCH
Aquamarine
APRIL
Diamond
MAY
Emerald
JUNE
Pearl / Moonstone /
Alexandrite
JULY
Ruby
AUGUST
Peridot
SEPTEMBER
Sapphire
OCTOBER
Opal / Tourmaline
NOVEMBER
Topaz / Citrine
DECEMBER
Turquoise / Tanzanite /
Zircon
1110
the following gemstones have been included as an introduction:
Gem materials are occasionally treated to
improve their appearance. the aim of treatments
is to strengthen colour, improve clarity,
accentuate phenomena, improve lustre or
improve durability of the stone. treatments
might affect the value of a gemstone so make
sure you check with the retailer.
When buying gemstones, you might also come
across ‘simulants’. these can be artificial stones,
that imitate the appearance of gemstones
without having their chemical composition,
physical properties, or structure.
many important natural gemstones, including
ruby, sapphire, and emerald, have man-made
counterparts that are manufactured in a
laboratory. such materials are called synthetic.
In all cases your jeweller should disclose
whether they are selling a gemstone,
a simulant or a synthetic.
the faceting & fashioning of gemstones the care & cleaning of gemstonesthe objective of cutting, sculpting and polishing
transparent gemstones is to show their fine glassy
polish, transparency and translucency. there are
many classic gemstone outlines. among the best
known, are: ovals, rounds, cushions, emerald cut,
pears, marquise, squares, triangles and cabochon
style cuts. Other gem shapes, including trapezoid
and hexagonal, or those with a free-form style, are
referred to as a fancy shapes. Within these outlines,
a vast array of facets, and facet combinations are
seen in gem materials. In turn, these combinations
help dictate the color, reflection and beauty that is
observed in gems. Because so much skill is required
to successfully cut or carve gemstones, there are
a series of quality characteristics you can look for
when evaluating the quality of cut.
Overall appearance:
• Face-up: the faceted gemstone should have a
pleasing ‘face-up’ appearance. It should reveal a
homogenous, even reflectivity and color in the
gem.
• the gem shape should be proportional. If you
could imagine folding a gem in half, one half
should be a mirror reflection of the other.
Faceting detail:
• Polishing marks (fine, curved scratches that
cross an entire facet) should preferably not
be observed along the surfaces.
• Facet junctions, where the lines or corners of
one facet meet up with another, should also
be crisp, sharp and straight.
Rules-of-thumb for carved gems:
• In carved gems, proportionality is not as critical;
here the artist dictates the outcome of the gem.
• some carvings may be free form. Here the
quality and evenness of polishing is important,
especially along curved surfaces.
Gems mounted in jewelry are rare and
precious heirlooms that can be lovingly passed
from one generation to another. as with all
things of value, they do require special care
considerations. For example, while some gems
are harder or more durable than others, none
should be worn while performing rigorous
physical exercise, repetitive movements or
around heavy machinery. that is because a
hard knock could endanger any gem material.
the following care considerations are also
important:
Storage:
• a clean, dry storage container with a padded
base, such as a drawer, or a jewelry box should
be used to store gems and jewelry.
• It is best to store jewels separately – in such
a way that sharp edges of one gemstone cannot
scratch another.
• When traveling, it is best to separate jewelry
into separate boxes or plastic bags so that they
cannot rub against one another.
Cleaning:
• Whenever possible clean a gemstone with
a clean, dry cloth. lukewarm water or water-
diluted mild detergent moistened cloths may
also be used for stubborn fingerprints, soil or
stains. Densely woven microfiber cloths are
best to use, as cloth fibers are less likely to
be caught in a prong.
• Organic gems such as amber, bone, coral
and ivory are generally fairly soft and porous
relative to other gems, though most also
have excellent durability. With proper care,
these may last for generations. With all
organic materials it is best to avoid the use
of chemicals solvents to clean a gem.
• ultrasonic cleaners use high frequency
vibration capable of dislodging debris and
soil that is hard to get to in jewelry. still, it
might be a better idea to reach debris with
a soft bristle toothbrush and running water.
While most gems can be cleaned this way,
it is prudent not to submit softer or more
porous gems to ultrasonic cleaners.
1312
understanding natural pearls, cultured pearls and imitation pearlsTyPes Of Pearls
today there are four types of ‘pearl’, these are
the rare natural pearls, the rare cultured pearls
that have not been subject to treatments, the
common cultured pearls where the appearance
has been artificially modified and the common
imitation pearls.
natural pearls are accidentally formed in
the interior of a mollusc without human
intervention and may be nacreous or non-
nacreous.
Cultured pearls are also formed within
molluscs but with the intervention of man,
the overwhelming majority being nacreous.
Imitation of pearls are artificial products not
formed in molluscs but manufactured by man
to only imitate the appearance, colour and
other features of natural or cultured pearls.
It should be noted that the practice of
artificially modifying natural and cultured
pearls to remove blemishes or to improve
their appearance has existed for centuries.
However with modern processing techniques,
this practice is standard procedure today for
the vast majority of common cultured pearls.
naTural Pearls
Nacreous pearls
many historical documents show that mankind
has used nacreous natural pearls as ornaments
since long before the beginning of the Christian
era. In about 4,000 BC, the Indian Ocean,
the red sea and the arabian Gulf were famous
for being a rich source of natural pearls.
In addition, many freshwater natural pearls
were found in European countries.
after the discovery of america by Columbus,
numerous saltwater natural pearls were fished
from Venezuela, Central america and mexico.
later large quantities of natural freshwater
pearls would be found from the rivers and lakes
throughout north america. nacreous pearls may be white, grey to black but
also slightly cream to yellow. Its typical growth
leads to the succession of concentric layers of
nacre. the finest nacreous pearls show a typical
bright lustre and a vivid orient, a subtle play of
all rainbow colours.
From the 1930s the availability of new nacreous
natural pearls to the market contracted, largely
due to the discovery of oil in the arabian Gulf
and the evolution of pearl culturing.
nevertheless, fine jewellery containing these
unique products of nature continue to be
available to those who appreciate and desire
these wondrous and very special prizes. Indeed,
some important pearls now have significant
collector potential and have become the
centrepiece of displays in museums and
personal collections throughout the world.
Abalone pearls
the abalone produces some of the most
interesting and certainly the most colourful of
natural nacreous pearls. Only rarely found in
symmetrical shapes these baroque pearls lend
themselves to one of a kind designer jewelry.
much sought after as a food source, the abalone
is a gastropod widely inhabiting the Pacific,
atlantic and Indian oceans. the population is
particularly rich along the coastal areas of Japan,
north america, australia and new Zealand.
1514
One Of The fInesT examPles Of an amerICan naTural
freshWaTer Pearl neCklaCe and an equally fIne
sIngle Pearl
a unIque fIve rOW neCklaCe Of naCreOus salTWaTer
naTural Pearls
aBOve: a hOrn shaPed aBalOne Pearl
WITh a rare rOund shaPed examPle
BelOW: a lOng aBalOne BlIsTer Pearl
sTIll aTTaChed TO ITs shell
Non-Nacreous pearls
there are several wonderfully fascinating non-
nacreous pearls available in the market. these
are produced by a variety of molluscs and are
generally of natural origin. Conch pearls are
produced by a gastropod commonly known as
the ‘Queen‘ or ‘Giant conch’ (Strombus gigas)
that inhabits Caribbean waters. as with many
non-nacreous pearls, conch pearls differ from
nacreous pearls by having a tough crossed
lamellar microarchitecture that manifests
itself as a flame-like structure that appears
to move as “watered-silk” when the pearl is
moved under light. Be aware that cultured
conch pearls have recently become available
and watch out for natural and cultured conch
imitations, which are produced by cutting the
thick conch shells into beads.
Other examples of non-nacreous pearls include;
the orange to reddish brown coloured horse
conch pearl produced by Pleuroploca gigantea,
a very large gastropod inhabiting Indo-Pacific
waters. the yellow to orange melo pearl produced
by the melo volutes and found in australian
waters, the south China sea, the waters around
the Philippines, the eastern coast of Indonesia
and the adaman sea. they are often spherical
and quite large but can also be baroque. Very
fine individual melo pearls have fetched very high
prices both in the trade and at auctions
CulTured Pearls
History
Cultured pearls are clear evidence of man’s
ability to merge with nature; they result from
a special relationship between man’s ingenuity
and nature’s ability to produce items of great
beauty. since their creation cultured pearls have
gradually become one of woman’s most popular
(and affordable) items of adornment; blending
with almost any fashion or skin type necklaces
of cultured pearls are today an indispensible
item in any personal jewellery collection.
there are many examples of ancient pearl
cultivation however; the modern pearl culturing
industry probably has its origins in or just prior
to 1890 when the first spherical cultured pearl
was produced by William saville Kent. While Kent
was the first to use the ‘tissue graft’ technique
to produce his spherical cultured pearls, the
first patent for this technology was actually
issued to the Japanese researcher nishikawa
by the australian Government on 24 July 1914.
subsequently, on 26 June 1916, nishikawa
was also granted a patent by the Japanese
Government. nevertheless, due to his worldwide
promotion and distribution of Japanese cultured
pearls, it is generally acknowledged that
mikimoto was the pioneer of the modern pearl
culturing industry. since then the modern day
cultured pearl industry has developed into a
significant if not the most significant presence in
the jewellery market, worldwide.
Varieties of cultured pearls
Akoya cultured pearls are cultured in Japan,
China and Vietnam using akoya oysters (P.
fucata (martensii)). Compared with other “pearl
oysters”, the akoya oyster is rather small;
hence the size of pearl produced is less than
10mm. the most popular sizes are 6 and 7mm.
akoya cultured pearls are generally bleached
in order to produce the uniform white seen in
most necklaces.
1716
akOya CulTured Pearls
varIOusly COlOured CulTured PearlsCOnCh Pearls frOm sTrOmBus gIgas
melO Pearls frOm One Of The melO vOluTes
South-sea cultured pearls are cultivated in
the oceans off northern australia, Indonesia,
and the Philippines using silver and gold-lipped
pearl oysters (P. maxima). the largest south-
sea cultured pearls and the majority of rare
cultured pearls are produced in australia waters.
the south-sea cultured pearls of Indonesia are
generally a little smaller than the australian
cultured pearls. the majority of golden (yellow)
coloured south-sea cultured pearls are produced
in the Philippines. Common south-sea cultured
pearls may be bleached, dyed or even heated to
achieve their appearance.
Black cultured pearls are cultivated in the black-
lipped pearl oyster (P. margaritifera) mainly in the
ocean around French Polynesia (tahitian cultured
pearls), but also in the waters of Fiji and the Cook
Islands, and in Pinctada mazatlanica or Pteria
sterna. rare tahitian Black cultured pearls exist in
a variety of natural colours from grey to black and
purplish green (known as “peacock green”) as well
as other colors including “pistachio”, dark blue,
“copper” and “cherry”. Common black cultured
pearls from tahiti may be bleached and/or dyed to
produce the recent “Chocolate” coloured pearls.
Freshwater cultured pearls are cultured in
lakes and rivers mostly in China, Japan, and the
united states. a freshwater cultured pearl is not
cultivated in a pearl oyster; but in a freshwater
mussel and generally this is without a bead, that is,
the process involves only a piece of mantle tissue.
approximately 40 (larger sizes) and maybe up to
100 (smaller sizes) cultured pearls are produced
by each freshwater mussel; this compares to the
norm of culturing one cultured pearl at a time per
pearl oyster. Chinese freshwater cultured pearls are
available in their natural colours, which are usually
white, orange and purple, but are mostly dyed to
almost any colour.
Quality elements
Size
most cultured pearls produced measure between
4mm and 8mm. the akoya beaded cultured pearl
ranges from 2 to 10mm. Freshwater non-beaded
cultured pearls range from 2 to 15mm. the south-
sea beaded cultured pearl (from P. maxima) and
the tahitian black beaded cultured pearl (from P.
margaritifera) range from 7mm to over 20mm.
Shape
there are many different shapes of cultured pearls:
shapes are generally described as being: round,
semi-round, oval, drop, button, semi-baroque,
baroque, and circled.
Nacre thickness
nacre thickness (the skin of the beaded cultured
pearl) is closely related to the type of mollusc
used, and the culturing period. the thickness of
the nacre covering the bead will determine the
durability of the cultured pearl. the quality and
thickness of the nacre will determine the lustre
and whether or not it possesses ‘orient’ – the
appearance of multiple but subtle colours.
Surface
the surface of a cultured pearl is examined in
terms of the number, size, kind and location of
imperfection(s). In evaluating imperfections, first,
the number of imperfections is taken into account
– whether a pearl has a clean surface, one spot
or many spots. then the kind of imperfection is
examined to determine whether there is a dent
or a bump on the surface; imperfections are
subdivided into pits, holes, pinpoints, bumps and
wells. Even if the imperfection seems insignificant,
if it is visible to the eye, it lowers the value of
the pearl.
Lustre
lustre, above all other aspects, is often regarded
as the most important characteristic of a cultured
pearl; it is an inextricable factor in defining a
cultured pearl’s beauty. lustre describes the
reflection of light from the cultured pearl. In rare
cultured pearls, lustre is created by the quality and
the thickness of the pearl nacre alone. ‘Orient’ (the
subtle array of colours found in rare cultured pearls
when light is refracted from within translucent fine
quality nacre) has a similar relationship with the
quality and thickness of the nacre. In the common
cultured pearl the impression of a high lustre is
created through the polishing process. a pearl with
good lustre will be bright and will have a sharp
reflection of light. a pearl with low lustre will be
dull and will have little or no reflection.
Colour
the colour of rare cultured pearls is only related
to the colour of the nacre of the host mollusc.
the colour of common cultured pearls may also
be related to the colour of the host mollusc’s
nacre, or will be a function of a dye artificially
applied to the cultured pearl during a treatment
or growth process.
1918
freshWaTer CulTured Pearls
varIOus levels Of surfaCe lusTre
In akOya CulTured PearlsBlaCk-lIPPed CulTured Pearls sIlver- and gOld-lIPPed CulTured Pearls
Overview of precious metalsthe best known precious metals are silver, gold
and the platinum group. the purity is measured
using a process called assaying, which, in simple
terms, means measuring the content of gold,
silver or platinum in the metal. Once an assay
office has determined the purity, they will stamp
a hallmark on the item to certify it.
gOld
Gold’s chemical symbol, au, is short for the latin
word for gold, ‘aurum’, which literally means
‘Glowing Dawn’. Pure gold has a bright yellow
colour and is one of only two coloured metal
elements, the other being copper. all other metals
are silver or grey. White golds are gold alloys that
look white rather than yellow. the white colour is
achieved by careful choice of the alloying metals,
which bleach the deep yellow of pure gold.
Caratage
Gold jewellery is usually described in terms of
‘caratage’ (‘karatage’ in the u.s.) to indicate its gold
content. this can also be described as fineness which
refers to the parts of gold per thousand by weight.
many countries only allow certain caratages of
gold jewellery to be sold. For example, in the
united Kingdom one can make and sell 9, 14, 18
and 22 carat gold jewellery, but not 12 carat gold.
In some countries jewellery lower than 12 carats
(50% gold or 500 fineness) cannot be described
as gold. the price of gold jewellery is based, in
part, on its gold content. Consequently, most gold
jewellery worldwide is marked with its caratage or
fineness, often as part of the hallmark. see across
for the appropriate levels in different jurisdictions.
Carats / Karats Fineness Gold content (%) Comments
24 999 99.9 Gold bullion
24 990 99.0 Minimum allowed for 24K gold
22 916 91.6 Indian subcontinent
21 875 87.5 Arabic countries
19.2 800 80.0 Standard in Portugal
18 750 75.0 Standard caratage
14 585 58.5 583/58.3% in USA
10 417 41.7 Minimum in USA
9 375 37.5 UK standard
8 333 33.3 Minimum in Germany
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PlaTInum
Platinum is one of the rarest of the precious
metals, found in only a few places worldwide
– principally south africa and russia. naturally
white; platinum will not fade or tarnish - keeping
its natural white colour forever. most platinum
jewellery is either 90% or 95% pure, does not
need rhodium plating and being hypoallergenic,
will not cause an allergic reaction. the density
of platinum gives it a heft and its ductile nature
allows craftsman to create the most intricate of
jewellery and its physical properties ensure that
precious gemstones are held securely. although
platinum may scratch like other precious metals,
minimal metal is lost, being merely displaced,
so a platinum piece will retain its metal weight
for generations.
The platinum group
the platinum group comprises six metallic
elements clustered together in the periodic table:
ruthenium, rhodium, palladium, osmium, iridium
and platinum. they are grouped together because
they have similar chemical properties.
Assaying
the usual method for assaying platinum is known
as inductively coupled plasma-optical emission
spectrometry. a sample of platinum is scraped from
the item to be tested, and then weighed on a highly
sensitive balance. the next stage is to dissolve the
sample in the appropriate acid matrix.
this solution is then passed through the
spectrometer, which determines the amount
of platinum present in the solution as compared
to the mass of the original sample taken.
Once the purity of the platinum is determined,
the item will be stamped with a hallmark to
certify this.
PalladIum
Palladium is one of the platinum group metals
but is considered a precious metal in its own right.
It is naturally white, which means there is no
need for rhodium plating.
It is more precious than silver and lighter than
platinum (nearly half the weight) so larger
necklaces and bracelets can be made capable
of bearing bigger gemstones with no gain in
overall weight. For the same reason palladium
is considered to be a good choice for earrings
although unlike platinum it is not hypoallergenic.
Assaying
the usual referee method for assaying palladium
is inductively coupled plasma-optical emission
spectrometry, the same as for platinum.
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sIlver
silver is a soft, white, lustrous transition metal
and is used in currency, ornaments and jewellery.
sterling silver is an alloy of silver containing 92.5%
pure silver and 7.5% other metals, usually copper.
Britannia silver is an alternative hallmark-quality
standard containing 95.8% silver, often used to
make silver tableware and wrought plate.
Hippocrates, the father of modern medicine,
wrote that silver had beneficial healing and anti-
disease properties, and the Phoenicians used to
store water, wine, and vinegar in silver bottles
to prevent spoiling.
Assaying
unlike gold, the usual referee method for
assaying silver is a process known as
‘potentiometric titration’.
a sample will be scraped from the item to be
assayed which weighs between 50 and 250
milligrams. the sample is then weighed using
a highly accurate balance and dissolved in
nitric acid.
In order to determine the silver content, potassium
chloride is added to the sample and the electrical
conductivity of the solution is tested until the
point that the ‘titration’ is complete and all of the
silver has become silver chloride. the amount of
potassium chloride needed to get to this point
indicates the amount of silver that was in the
original sample.
markIng and hallmarkIng PreCIOus meTals
It is impossible for anyone to know how much
precious metal there is in a piece of jewellery
simply by looking at it or touching it. the
precious metal content must be declared in
some meaningful way. all jewellery should
therefore be marked or hallmarked with a
stamp so that you know what you are buying.
Marking
as a minimum, all items of jewellery should
be stamped with a ‘fineness mark’ declaring
the content of precious metal in the alloy, and
a registered ‘responsibility mark’ indicating the
name of the trader who has first placed that
piece of jewellery on the market.
Hallmarking
some countries have independent third party
assay Offices who test precious metal jewellery
and then strike a ‘Hallmark’ on the article to
guarantee its’ fineness.
a hallmark, is a mark or series of marks struck on
items made of precious metals – platinum, gold,
silver and, in some nations, palladium. Hallmarks
are applied by an assay office and they guarantee
a certain purity or fineness of the metal.
national hallmarking systems differ from
country to country. the Vienna Convention of
1973 standardised the hallmarks, legislation
and inspection of precious metals in signatory
countries to facilitate international trade.
Because it is so widespread it is the best
example to illustrate how an independent
third party hallmarking system works.
articles which are assayed and found to be
in conformity by the qualifying office of a
member country receive a hallmark, known
as the Common Control mark, and can be
exported and immediately sold in any of the
Convention countries without further testing
the Common Control mark is a balance scales
symbol superimposed on:
Gold:
two intersecting circles
Silver:
the letter ‘m’
Platinum:
a diamond shape
Palladium:
a tent design
925
900
585
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