Jeweller - May 2019

GEMS
ORGANIC GEMS PART II: PEARLS
pearls, and Pteria penguin pinkish pearls with
the mabé shape.
The iridescence of the nacre can create
overtones of pink, green, purple or blue.
While the perfectly spherical pearl is highly
prized, each shape has its own beauty and
suits particular jeweller settings. These shapes
include button, oval, drop and baroque, as
well as mabé, which is a pearl that is flattened
on one side.
Keshi pearls are a little surprise of nature and
highly sought after due to their exquisite
lustre and unique freeform shapes. These
small baroque pearls are typically formed as
by-products of pearl cultivation.
Natural pearls are produced without any
human intervention and are extremely rare,
with almost all available pearls in the market
today being cultured by man. Culturing
involves ‘seeding’ live molluscs with a small
shell bead, upon which the creature forms a
nucleus and begins to secrete its nacre.
Known as ‘The Queen of Gems’, pearls
are our gems of the sea. These lustrous
creations have been loved and admired
throughout different cultures across
thousands of years. This organic gem is
produced within the soft tissue of certain
species of molluscs and is found in a
variety of hues and forms.
Pearls are rounded concretions composed
of calcium carbonate – specifically aragonite
and calcite – and organic matrix, secreted
from particular marine and freshwater
molluscs. There are two kinds: nacreous and
non-nacreous.
The surface of a nacreous pearl is formed
from thin layers of nacre, or mother-of- pearl,
that are deposited as microscopic, tile-like
crystals. The iridescence produced by a pearl’s
nacre is caused by the diffraction of white
light as it interacts with the arrangement of
these aragonite crystals.
Non-nacreous pearls may be produced by
the pink or queen conch (Strombus gigas),
the giant clam (Tridacna gigas) and several
species of edible oyster. They do not display
an iridescent surface. Instead, these pearls
commonly have a porcelain-like appearance
due to their calcite or mixed calciticaragonitic
composition. They are still admired
for their pale colours and lustrous surfaces
and are used for both jewellery and art.
The quality factors of a pearl may be
broken down to: shape and size, body
colour, iridescence, lustre and the presence
and intensity of the ‘orient’ – a dramatic,
multicoloured iridescent sheen.
The body colour of a pearl is thought to be
caused by organic pigments present in the
matrix. The most familiar colours of nacreous
pearls are white and cream. They may also
be black, grey and silver. Pinctada maxima
oysters tend to produce silver or champagne
pearls, Pinctada margaritifera produce black
A GEM THAT
DOES NOT
REQUIRE FURTHER
POLISHING
OR FACETING
TO ENHANCE
ITS BEAUTY, A
PEARL IS SIMPLY
PERFECTION IN ITS
NATURAL FORM
– THEIR DELICATE
IRIDESCENT SHEEN
IS CAPTIVATING
Commercial production of cultured pearls
began in the early 20th Century and has
changed a great deal since. Whilst there is a
level of control over the size and shape of
the pearls cultivated, the mollusc is still very
much in charge of the process, alongside the
forces of nature.
A gem that does not require further polishing
or faceting to enhance its beauty, a pearl is
simply perfection in its natural form. Their
delicate iridescent sheen is captivating
and can be enhanced by the presence of
other gems or simply dazzle on its own.
Beautiful as single spherical shapes, baroque
forms or long strands, pearls are a classic
jewellery staple. i
STACEY LIM FGAA BA Design, is a qualified
gemmologist and gemmology teacher/assistant.
She is a jewellery designer, marketing manager
and passionate communicator on gemmology.
For information on gemstones, visit: gem.org.au
May 2019 Jeweller 33