Pearl Nacre Thickness

Nacre is a pearly substance that mollusks secrete around irritants.

Nacre thickness is not as important a price factor for natural pearls and cultured freshwater pearls as it is in cultured saltwater pearls because natural pearls and cultured freshwater pearls have no shell nucleus or are nearly all nacre. One of the biggest selling points of cultured freshwater pearls is that they usually have a higher percentage of pearl nacre than their saltwater counterparts. However, it's of critical importance in cultured saltwater pearls. The thicker the nacre coating of a pearl is, the more lustrous and durable the pearl; the thicker the pearl nacre layer is, the more valuable the pearl. Nacre thickness is one of the most important quality factors for cultured saltwater pearls because it affects both pearl beauty and durability. South Sea pearls normally have a thicker nacre coating than Akoya pearls.

Thick, overlapping nacre layers create a strong luster and a valuable pearl. Thick nacre layers take years to build up. It can be used to determine whether a pearl is real.

Nacre thickness is classified by the following standards:

Very thick: A ≥0.6mm
Thick: B ≥0.5mm
Medium: C ≥0.4mm
Thin: D ≥0.3mm
Very thin: E £¼0.3mm

Perlunna pearls on sale all are above 0.5mm in nacre thickness.

Judging Nacre of Pearls

Sometimes you can know the nacre by looking at the pearls to determine if it's thin or very thin. The thin-coated pearls usually have a low or very low luster and may look milky. Areas are visible where the nacre has peeled off or cracked.

1. A more accurate way of judging nacre thickness is by examining the drill holes of the pearls, preferably with a 10-power magnifier such as a jeweler's hand loupe. Examining drill holes with a loupe will also help you detect dyes and imitations. The drill-hole method is too slow to be practical for dealers, but it is a good way for less-skilled people to estimate nacre thickness. It also allows appraisers to give a more objective measure of nacre thickness.

2. As the beads are rolled, some may look light and then dark as the light shines through them. This is because the shell beads may have mother-of-pearl layers that block the light. This phenomenon is called "blinking" and can sometimes be seen in thinly coated pearls. Pearls with thick nacre should not blink.

Ideally, consumers could choose from a wide range of nacre thicknesses and know exactly what they were getting for their money. Since this ideal does not currently exist, it's to your advantage to pay attention to nacre thickness and to learn to detect thin nacre yourself.