L

Layer
One layer of nacre equals approximately one micron, or one thousandth of a millemeter. The Polynesian Pinctada Margaritifera oyster secretes three or four concentric layers a day. After two years, the layer will be up to 2.5mm thick, while the Japanese Akoya oyster will secrete a layer less than 1mm thick.

Luster
This term comes from the Latin world lustrare, which means to light. The shine of the pearl is due to two combined phenomena:
° Surface luster: the reflection of light on the surface of a pearl, which can be reduced by erosion or increased by polishing;
° Deep luster: caused by the passage of light through the layers of nacre. The thinner, more regular and transparent the layers are, the better the luster is.