Mother of pearl or Nacre is the shimmery coating on the inside of certain mollusk species. This iridescent layer is made of aragonite and calcite (calcium carbonate polymorph). Mother of pearl has many commercially utilities including pearl nucleus manufacturing. Mother of pearl is exclusively found in some of the older lineages of gastropods (Trochidae, Turbinidae and Haliotidae), cephalopods and bivalves. However, most mollusks have a porcellaneous inner layer, not nacreous. This type of layer has a non-iridescent shine, or non-nacreous iridescence. Inner layers of pearl mussels and pearl oysters are made of mother of pearl.
Mother of pearl was extensively used by ancient Egyptians for various decorative purposes. Its use dates back to more than 4000 BC, although the use of actual pearls started only after 5th century BC. In 2300 BC, Chinese regarded Mother of Pearls as prized possessions. In India, ancient Hindus believed that god Krishna discovered the first Mother of Pearl. Ancient Romans regarded mother of pearl as a symbol of wealth and prestige. The ancient Greeks used them especially at weddings. They believed that mother of pearl ornaments bring love. Ancient Roman historian Pliny the Elder (23 AD – August 25, 79 AD) described the most celebrated episode in Roman history involving pearls in his book, “Natural History”. Cleopatra, the last Egyptian queen, arranged for a banquet for the Roman leader Marc Antony. The story goes like this: Cleopatra challenged Marc Antony that she could afford to give the most expensive meal ever provided. In a vessel of sour wine, Cleopatra dropped one of her mother of pearl earrings. It was worth of 10 million sesterces. Strong acidic solution dissolved the pearl. Cleopatra drank it and won the bet. The United States become the major exporter of mother-of-pearl. Mother of pearl was used to make iridescent clothing buttons. Billions of buttons were exported all over the world from Iowa. This business lasted till the mid-20th century. Later, it was replaced with plastic products.
Mother of pearl consists of hexagonal aragonite platelets which are arranged in parallel lamina. Organic matrix made of elastic biopolymers separate these layers. The blend of elastic biopolymers and brittle platelets makes mother of pearl resilient, as well as strong. It can be black or white colored. The aragonite platelets’ thickness closely resembles the visible light’s wavelength. As a result, there is a destructive, as well as constructive interference of various wavelengths of the light. Different colors are reflected at various angles of viewing which makes the mother of pearl shine brilliantly.
The epithelial cells present in the mollusk’s mantle tissue produces mother of pearl to protect itself from harmful parasites. Nacre is deposited constantly on the shell’s inner surface. It protects the soft tissue from external debris and parasites by entombing them in successive layers of nacre. It leads to the formation of a free pearl or a blister pearl within the mantle tissues. The secretions of Nacre is a defense mecahnism in the mollusk. This mechanism is known as encystation. This process continues as long as the mollusk is alive.
Mother of pearl has been used for various decorative purposes. Both black, as well as white mother of pearl is used in architectural decorations. It can lightly tinted with other colors. Mother of pearl tesserae can be cut into various shapes and laminated to a marble base or ceramic tile to create an irregular pattern or mosaic. Mother of pearl tesserae is polished and lacquered to create a glossy, as well as durable surface. Light-weight sheets of mother of pearl can be used on walls, interior floors, doors, ceiling and countertops. Mother of pearl is also used in the world of fashion. Buttons made of nacre are used in all types of clothing. Mother of pearl is also used for decorating jewelry, watches, guns and knives. It is also used for decorating different types of utensils such as spoons and bowls.