If you look closely at the surfaces of precious stones and minerals, you will notice that light is reflected in several unique ways – a property known as luster. Luster describes how light dances across a surface and helps mineralogists classify and identify the varied stones. Luster is organized by degree (grading from high to low) and category. Common categories range from metallic, greasy and resinous, to silky, glassy and (our favorite): pearly.
High luster is the hallmark of quality natural or cultured pearls. Across a pearl type (whether akoya, South Sea, golden South Sea, or freshwater pearls) when all other value factors are equal, the higher the luster, the more valuable the pearl. Tightly stacked layers of a calcium carbonate material called nacre form the basis of a pearl and are the reason we enjoy this brilliant phenomenon. Thicker layers of nacre increase the prominence of luster. Natural pearls and baroque cultured pearls often display the most dramatic flashes of luster – a byproduct of the deep pools of nacre that collect on those pearls’ surfaces.
Luster refers to the way a pearl’s surface reflects light and also to the way it refracts light. The combination creates a soft glow that is unique to pearls among other precious gems. Because luster is a measure of quality, it also influences price. Here are some tips when evaluating pearl luster:
- Pearls with high or excellent luster have reflections that are crisp, bright and distinct. You will be able to see your reflection quite clearly on the surface of the pearl.
- Pearls with good luster will reflect brightly, but not as distinctly. Edges or details in the reflection may appear slightly blurred.
- Pearls with fair luster reflect weakly and often appear hazy or smoky.
- Pearls with poor luster are often described as dull or chalky. Reflected shapes are not distinguishable on the pearl surface. This may be an indication of thin nacre and insufficient time forming within the oyster.
A reputable jeweler like Spey will be able to guide you along the path of selecting pearls of exceptional luster. The gentle glow is an immediate indicator of quality and is readily recognizable to pearl aficionados. Pearls are a gentle, quiet luxury – and luster lends them their brilliance.