Every pearl is unique and the revered beauty of the pearls is in their individuality.  Grading and valuation of pearls is infinitely difficult although it is accepted that the following criteria be evaluated:

Lustre - the lustre of the pearl is its refraction of light through the depth of the nacre.  Nacre is the natural secretion from the oyster that makes up the pearl.  The thickness of the nacre creates the lustre of the pearl.  Healthy oysters, which have been meticulously farmed and afforded the necessary time to lay down substantial layers of nacre, will produce the highest lustre.  Quality pearls with high lustre will stand the test of time to be enjoyed by generations to come.

Complexion - every pearl is unique and most pearls will have some small imperfection on their surface, pearls with less or no imperfections are more highly valued.

Shape - the shape of each pearl depends on how evenly or unevenly the oyster lays down the nacre during its cultivation period.  Pearls are most often produced in round, near round, tear- drop and baroque shapes.  Round pearls are the most highly valued.

Size - size of the pearl is dictated according to the species and size of the oyster and size of the implant.  The South Sea Oyster (pinctada maxima) produces by far the largest pearl.  The oyster may produce between one and three pearls during its lifetime.  With only some of the oysters living long enough to produce a third pearl, which is likely to be the largest pearl that oyster will produce, these larger pearls are more highly valued for their rarity.  Pearls are generally measured using a milliguage and sometimes by sieve, depending on the shape of the pearl.  The weighing unit for pearls is momme, an old Japanese measure of weight still used for all pearls.  One momme is equal to 3.75 grams or 18.75cts.