Pearl Lustre:
Lustre is the most important determinant of beauty and value of a pearl of any type.
Definition of Pearl Lustre:
Lustre is describe as the combination of:
- The surface brilliance (amount of light reflected from the pearl’s surface). Gauge of surface polish. Lustre and surface smoothness are equally important criteria.
- The glow emanating from deep within the pearl.
With all pearls:
- Under a bare light, roll the pearls against a white background
so you can see their entire surface area.
- Describe the intensity of the lustre--high lustre to low lustre. Ranges from bright and sprightly to warm and alluring. To judge lustre, look at pearls ranging from very low lustre to very high lustre.
In High Quality Pearls:
- The lustre is high
- The lustre is evenly distributed
- High contrast between the light and dark areas of the pearl
- A good quality pearl will have a lustre that is bright, not dull
- Should be able to see your reflection on the surface of the pearl
- Reject pearls with a low intensity of lustre
The Relationshipbetween Lustre and Nacre Thickness in Different Pearls:
- Mikimoto Co. put nacre thickness as one of the most important factors (along with lustre) in the beauty and durability of the pearl. Nacre quality is determined by its thickness and layering.
- In general, the thicker the nacre, the more valuable the pearl. If a pearl is large, this doesn’t necessarily mean that the nacre is thick. And a small pearl, may have thick nacre. X-ray is the best way to determine the nacre thickness of a pearl. This is worthwhile only if you are spending thousands of dollars.
- Buy pearls that have a high lustre.
In Akoya Pearls:
Especially in akoya pearls, lustre is closely associated with nacre thickness.
- If a white pearl has a high lustre, this usually means that the nacre is thick
- If it has a low lustre the nacre thickness is usually thin.
- Nacre quality is determined by its thickness and layering of nacre. Inspect a pearl for the thickness of nacre. A pearl's nacre is too thin if the core nucleus is visible. This pearl should be rejected.
- The surface polish or lustre may have a chalky appearance due to thin nacre or poor nacre layering
In Black Pearls:
- Pearls with a good lustre can have thin nacre and those with a poor lustre can have thick nacre.
- This is because dark nacre does not reflect light in the same way that white
nacre does. Some black pearls can look almost metallic.
- With black pearls, you must treat lustre and nacre thickness as two separate value factors.
In South Sea Pearls:
- White South Sea pearls have a lower lustre potential than Akoya and Black pearls.
- As mentioned previously, big pearls do not necessarily have thick nacre. However, good South Sea pearls should have a nacre thickness of at least 1mm of the radius. Thin nacre in a South Sea pearl is not easily detected.
In Freshwater Pearls:
- Nacre thickness is not as important of a factor in cultured freshwater pearls as it is in saltwater pearls. This is because most freshwater pearls do not have a shell nucleus. When one is present, the nacre tends to be thicker. One of the biggest selling points of freshwater pearls is that they usually have a higher percentage of pearl nacre than their saltwater counterpart.
