Mother of pearl, also called nacre, is the shimmering inner lining of some mollusc shells. Watchmakers use it to make dials. It has a rainbow sheen, and every shell has its own pattern, so no two mother-of-pearl dials look the same.
What is mother-of-pearl made of?
Nacre is part organic and part mineral. Its mineral part is made of tiny six-sided plates of aragonite, which is a form of calcium carbonate. Each plate is about as thick as a wavelength of visible light. This is what produces the rainbow shimmer. Pearls are made of the same material. In a shell, nacre forms the inner lining.
Where it comes from
Only some molluscs grow nacre as the inner layer of their shells. Most shells have no nacre lining and a porcelain-like inner layer instead. Commercially, mother-of-pearl has mainly been harvested from pearl oysters and freshwater pearl mussels. It is also often found in abalone shells. For watch dials, the Pteria margaritifera shell from Australia is considered one of the best sources.
How are mother-of-pearl dials made?
Nobody can say exactly when watchmakers first used mother-of-pearl. One way to make a dial is to crush the shell and machine it into discs only about 0.2 mm thick. Coloured lacquer can then be applied to the back of the disc. This can strengthen the dial’s colour or change it. At this thickness the material is brittle and breaks easily. Because every shell is different, every dial is different too.
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