Also known as Nacre, is an organic–inorganic composite material produced by some molluscs as an inner shell layer; Mother of pearl is found in the outer layer of cultured pearls and the inside layer of pearl oyster and freshwater pearl mussel shells. It is strong, resilient, and iridescent.
Nacre is secreted by the epithelial cells of the mantle tissue of various molluscs and continuously deposited onto the inner surface of the shell. The layers of nacre smooth the shell surface and help defend the soft tissues against parasites and damaging debris by entombing them in successive layers, forming either a blister pearl attached to the interior of the shell, or a free pearl within the mantle tissues. The process is called encystation and it continues as long as the mollusc lives.
Scientists from the University of Michigan and Australia’s Macquarie University crushed a miniscule mussel and used an electron microscope to observe the effects. Under compression, nacre’s binding organic layer dissipates to areas of lower pressure (like squeezing a bag of liquid and the liquid moves to everywhere but where you’re squeezing). Once decompressed, the structure fully restores its original build and mechanical strength as the organic material fills back in.
Its remarkable strength and ubiquity might shed some light as to why Mother of Pearl has been one of the most common materials used for bead making, adornment, and trade by several civilizations across the world, such as Ancient Egyptians, Mesopotamians, Native Americans and in China during the Bronze Age of the Shang dynasty.
It reached its height in the 19th century, when all manner of items featured the material, including inkwells, snuff boxes, fans and card cases.