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ize, shape and qual­ity are used as the bench­marks for grad­ing black pearls and only those of Grade C and above qual­ify as Avaiki pearls.

There are three cat­e­gories: spher­i­cal, sym­met­ri­cal and non-sym­met­ri­cal. Gen­er­ally, spher­i­cal pearls are the most val­ued and in­clude rounds and semi-rounds. Sym­met­ri­cal shapes in­clude cir­cles, drops, ovals and but­tons. The non-sym­met­ri­cal are known as baroque and semi-baroque.

Many lay­ers of nacre built up over time form a sur­face that is eval­u­ated ac­cord­ing to smooth­ness and the pres­ence of im­per­fec­tions. As pearls are cre­ated by liv­ing or­gan­isms, per­fec­tion is rare. Like our hu­man skin, slight im­per­fec­tions of­ten oc­cur in the form of marks, spots, ridges and colour in­con­sis­ten­cies.

In the Cook Is­lands, pearls tend to range on av­er­age be­tween 10mm and 13mm, although very oc­ca­sion­ally a pearl may reach 18mm. With the ex­cep­tion of the but­ton shape, the size is de­ter­mined by the mea­sure­ment along its short­est axis and in whole mil­lime­tres to rep­re­sent one size cat­e­gory.

A pearl’s lus­tre is the in­tense bright­ness cre­ated as light trav­els through the many lay­ers of nacre and is re­flected back to the eye. Eval­u­a­tion de­pends on the de­gree of bright­ness, which is in­flu­enced by the thick­ness of the nacre. Ori­ent is the iri­des­cent, shim­mer­ing play of colour that oc­curs when the nacre is par­tic­u­larly thick and well­formed. Vis­i­ble when the pearl is ro­tated, it too adds value to the pearl.

Black pearls come in a wide va­ri­ety of shades that mir­ror the rain­bow-like spec­trum found in the mother-of-pearl shell. The darker hues of black, blue, green and brown are prom­i­nent, while lighter colours such as white, sil­ver, grey and gold are also ev­i­dent. Be­sides these body colours, higher-qual­ity pearls re­veal translu­cent over­tones that ap­pear over the pearl’s body colour and cre­ate in­ter­me­di­ary shades such as aubergine, pea­cock green and lighter pas­tels. They also add depth and glow. Colours do not usu­ally in­flu­ence the grad­ing of an in­di­vid­ual pearl but cer­tain rarer colours do at­tract higher prices.

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