Nacre (pronounced “NAY-ker”) is the smooth, shimmering material that lines the inside of certain seashells and forms pearls. You might know it better as mother-of-pearl, that rainbow-colored coating you see inside an oyster shell or an abalone shell.

Nacre forms when a mollusk (a sea creature like an oyster or mussel) secretes thin layers of minerals and proteins. These layers stack thousands deep, each one microscopically thin. Light bounces between these layers, creating that characteristic shimmer where colors seem to shift as you tilt the shell. This optical effect, called iridescence, makes nacre catch pinks, blues, greens, and silvers all at once.

When an irritating grain of sand or parasite gets trapped inside an oyster's shell, the mollusk coats it with layer after layer of nacre to protect itself. Over months or years, this process creates a pearl. Natural pearls are rare and valuable because this happens by chance, though modern pearl farmers deliberately introduce an irritant to encourage oysters to make pearls.

For thousands of years, people have carved nacre into buttons, jewelry, and decorative inlays. If you've seen an acoustic guitar with shimmering designs around the sound hole, that's probably nacre inlay. The material is both beautiful and remarkably strong for something produced by a soft-bodied sea creature.