Nacre n. : A pearly substance which lines the interior of many shells, and is most perfect in the mother-of-pearl. [Written also nacker and naker.] See Pearl, and Mother-of-pearl.

Example:
Nacre? Where can I get some Nacre, for 'painting' and repairing 'pearls' on costume jewelry?

Taxonomy
nacre, mother of pearl, shell, layers, tesserae, free encyclopedia, nacreous layer, inner shell, mollusk, mollusk shells, shell layer, hexagonal platelets, sheets, thin layers, pearl buttons, decorative purposes, search, novel.

Defination from the web:
Nacre is found in some ancient lineages of bivalve gastropod and cephalopod. ... Pearls and the inside layer of pearl oyster and freshwater pearl mussel shells are made of nacre. ... The nacre is continuously deposited onto the inner surface of the shell, the iridescent nacreous ...