Grows inside a living mollusk and is judged first on luster, its glow from below the surface.
Also called: freshwater pearl, faux pearl, cultured pearl
Measurement
Mohs 2.5 to 3.5
The basics
What to know about pearl
A pearl is the only gem produced by an animal. Layer on layer of nacre, a mix of aragonite crystals and protein, builds around an irritant inside an oyster or mussel over months to years. Those layers are why a good pearl seems lit from within. Light passes into the translucent stack and reflects back. That effect is the property graded as luster and the first thing to judge.
The rest of the grade is surface cleanliness, shape, color, size and nacre thickness. Sizes follow type: freshwater pearls often run 5 to 10 millimeters, Akoya 6 to 8 and famously round, South Sea 9 to 16. Nacre thickness is the figure sellers rarely print and the one that decides lifespan. A bead nucleated pearl with a thin coat eventually wears through to the bead. Real nacre feels slightly gritty against a tooth edge; a coated imitation feels glassy.
At Mohs 2.5 to 3.5 a pearl is softer than a coin. Acid is the real enemy: perfume, hairspray, lemon, vinegar and chlorine dissolve nacre, and the dulling cannot be polished out at home. Put pearls on last and take them off first, then wipe them with a soft damp cloth. Strands should be knotted between pearls in silk and restrung every year or two with frequent wear, since silk stretches and absorbs body oil.
In photos
Pearl on real products
See this option on different products. Open a photo for a larger view, or select the name to read its guide.
Almost every pearl sold today is cultured, which means a farmer starts the process rather than waiting for chance. A technician opens the mollusk and inserts one of two starters. Akoya and South Sea pearls get a small round bead cut from shell together with a piece of donor mantle tissue. Tissue alone is how most freshwater pearls are grown.
The animal responds as it would to any irritant, coating the intruder with nacre from the same tissue that lines its shell. It goes back into the water in a net or basket, where farmers clean and turn it for anything from six months to several years. One harvest yields a wide spread of quality, so the pearls are washed, sorted by size, shape, color and luster, then drilled. Bleaching and mild polishing are common and normally disclosed.
Best for
When it works well
Bridal and classic dressing use pearls because the surface glows rather than flashes, which photographs softly.
Tailoring is softened by a strand, so pearls work where a bright stone would look severe.
Occasional wear suits them, since the softness that makes them vulnerable matters less when they spend most days boxed.
A first serious jewelry set often starts here, as a good strand costs far less than an equivalent gemstone.
