A Guide to Pearl Qualities and Grades

Buying pearls can be confusing - there are many myths, misconceptions and misleading pieces of information (see buying pearls - tricks and traps). One thing is certain. The romantic image of the pearl fisherman diving off the side of a small boat to harvest pearls from the ocean floor is gone. Wild pearls still exist but are difficult to find. Nowadays, pearls are cultivated in freshwater lakes and rivers or seawater rafts.

   Pearl Guide
pearl history a brief history of pearls
how pearls are formed how pearls are formed
pearl qualities and grades pearl qualities and grades
pearl shapes and colours pearl shapes and colours
pearl sizes pearl sizes and comparisons
choosing and caring for pearls choosing and caring for pearls
buying pearls buying pearls - tricks and traps
near round
mostly round
< 75% clean
> 75% clean
> 95% clean
0.25 to 0.35mm
0.35 to 0.5mm
over 0.5mm
very good
Pearl Grading takes into account shape, lustre, surface quality, nacre thickness and matching on the strand.

There is no international standard for grading pearls so identical pearls may be graded differently by different suppliers.

Grading a strand of pearls like a necklace is slightly different to grading individual pearls as not every pearl on the strand will necessarily meet all the criteria for that grade.

Pearls have their own jargon but most reputable pearl sellers use the A, AA, AAA grading system (Tahitian pearls may also use an A to D system) and follow accepted industry conventions.
Shape: pearls develop into a variety of shapes. Round pearls are the rarest and command the highest prices. The term 'round' does not mean spherical like a marble but the pearls should not be obviously oval or flattened to the naked eye.
pearl shapes
It's worth remembering that non-round pearls can offer a lot of pearl for your money. Wild pearls were rarely round so different shapes could be thought more natural.
Nacre: seawater pearls are cultivated by implanting an oyster with a mother-of-pearl shell bead. This is called the 'nucleus'.

To protect itself, the mollusc coats the bead with layers of nacre. The longer the bead stays in the oyster the more the layers of nacre and the finer the pearl.

seawater pearls Seawater pearls remain in the ocean for around two years to develop sufficient layers of nacre.

If a pearl is harvested too early the nacre covering the bead will be thin and prone to cracking and flaking.

Nacre thickness is one reason seemingly identical pearls may be priced differently.

On seawater pearls look for a nacre covering of at least 0.3mm, preferably 0.5mm plus.

Freshwater pearls use a different culturing technique and take up to six years to grow.

freshwater pearlsFreshwater molluscs are implanted with small pieces of tissue rather than a shell bead. When harvested, the tissue has gone, leaving a solid pearl.

Nacre thickness is not an issue with this type of pearl. They will not wear out.

Lustre is the shine that gives pearls their beauty and is an important buying factor. Lustre refers to the pearls brilliance - the way it's surface reflects light, and to it's inner glow - how it refracts light from the layers of nacre within.
pearl lustre
Pearls with low lustre appear chalky, yellow or dull rather than shiny. This example gives an idea of the lustre expected from different grades.

Poor lustre pearls are sometimes coated or laquered to improve their appearance but such treatments are only a temporary fix.
Surface Quality: pearls are a natural product and, like handblown glassware, small natural imperfections are quite acceptable. Unacceptable faults include cracks or holes in the surface or thin and flaking nacre.
pearl blemishes

Grade AAA at least 95% clean
Grade AA at least 75% clean
Grade A less than 75% clean

Pearls which are completely clean - with no scratches, pits, bumps or wrinkles visible to the naked eye - may be designated 'spotless'.
Matching compares all the pearls on the necklace with each other to see how they match. They don't have to be identical. That can seem artificial and real pearls will vary a little. Most people can judge when something looks wrong. Like, for example, a necklace of 7-8mm pearls where the bigger pearls are grouped to one side or a small pearl is sandwiched between two large ones.
pearl matching
Examine a necklace by placing it on a light cloth background in soft natural daylight. Not indoor lighting, UV display lights or direct sunlight. Is the lustre good or are the pearls chalky, yellow or dull ? Naturally coloured necklaces may have small variations in colour and tone but these shouldn't be glaring.

Turn the necklace in your hands and inspect it from different angles. Use the grading factors above to make a judgement but don't overdo the analysis. If it looks ok it probably is !
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