Jeweller - June, Edition II 2020

REVIEW
Gems
Ruby: the true red
Desire for ruby today is as great as ever.
With fluctuating quality and supply, and a
high demand for stones over one carat,
this blazing beauty can demand the highest
price per carat of any coloured gemstone.
Once thought to have held the power
of life due to its likeness in colour to
blood, rubies are still a highly coveted
gemstone, signifying wealth, success,
love and passion.
Ruby is the red variety of corundum, a
crystalline form of aluminium oxide.
Colourless in its purest state, corundum
is ‘allochromatic’ – meaning it relies on
trace impurities to influence its colour.
For ruby, chromic oxide replaces some of
the alumina in the crystal structure.
The amount of chromium present
determines the strength of ruby’s red,
while the presence of other elements,
such as iron, influence tone and hue.
Other than the orange-red through to
strong purplish red stones, which are
called ruby, gem quality corundum is
known as sapphire, prefixed by its colour.
Paler reds or pinks are thus appropriately
named pink sapphire.
The finest, rarest quality rich-red
Burmese rubies come from the
Mogok (old source) or Mong Hsu (new
source) mines.
These chromium-rich crystals form in a
white marble and because they contain
no iron, the result is vivid pinky-red
stones that can show fluorescence in
sunlight, adding to their intensity and
value.
In comparison, the rubies of Cambodia
and Thailand originate in iron-rich basalt
and are typically darker.
These stones have an orange-red
colouring because the iron impurities
diminish the vividness caused by
chromium.
In the past eight years, Mozambique
– a location of recent ruby discoveries
– have become a dominant source of
commercial quantities of varying quality
and colour.
African supplies have traditionally
produced darker stones, however the
new mines produce colours that bridge
the gap between those from the classic
sources of Myanmar (low iron, strong
fluorescence) and Thailand/Cambodia
(high iron, low fluorescence) suiting a
range of different markets.
A ruby’s value is determined not only
by colour, but its clarity, cut and carat
Ruby
From Latin ruber,
meaning ‘red’.
Colour: Red
Found in: Thailand,
Myanmar (Burma),
Cambodia, India,
Afghanistan, Brazil,
Namibia, Madagascar,
Pakistan, Vietnam
Mohs Hardness: 9
Class: Corundum
Lustre: Vitreous,
adamantine
Formula: AI 2
O 3
size. Consumers must be aware of the
multitude of treatments and synthetics.
Heat treatment is common practice as it
parallels what can happen in nature.
The heating process removes silk
inclusions, enhancing clarity and richness
of colour.
Although it does affect the price, if heat
treatment does not add anything artificial
to the stone, it is an accepted treatment
amongst gemmologists.
In more recent years glass has been
used to fill fractures in rubies, but while
the stone is made more attractive, the
glass fill can dramatically decrease its
durability.
Sometimes called ‘composite rubies’
– but more accurately ‘glass fracturefilled
natural ruby’ – the nature of such
stones should be explained and priced
accordingly.
Interpretation of colour may be subjective,
but there is no denying the beauty of an
intense red ruby.
The dominance of treated stones on the
market however, means that consumers
should trust their local Gemmologist or
Registered NCJV valuer to ascertain their
true identity.