Nacre pronounced also known as mother of pearl, is an organic-inorganic composite material produced by some mollusks as an inner shell layer. It is very strong, resilient, and iridescent.Nacre is found in some ancient lineages of bivalve gastropod and cephalopod. The inner layer in the great majority of mollusk shells is porcellaneous, not nacreous, frequently resulting in a non-iridescent shine or less commonly in non-nacreous iridescence such as flame structure (e.g. conch pearl).Pearls and the inside layer of pearl oyster and freshwater pearl mussel shells are made of nacre. Many other families of mollusk also have an inner shell layer which is nacreous, including marine gastropods such as the Haliotidae, the Trochidae and the TurbinidaeBoth black and white nacre are used for architectural purposes. The natural nacre may be artificially tinted to almost any color. Nacre tesserae may be cut into shapes and laminated to a ceramic tile or marble base. The tesserae are hand-placed and closely sandwiched together, creating an irregular mosaic or pattern (such as a weave). The laminated material is typically about 2 mm thick. The tesserae are then lacquered and polished creating a durable and glossy surface. Nacre inlay is often used for key touches and other decorative motifs on musical instruments. Synthetic key touches made of Pyralin or similar imitation nacre materials such as celluloid have been affectionately referred to as mother of toilet seat.[citation needed] Many accordion and concertina bodies are completely covered in nacre.