Jenny Marie Eskew, age 11, of Wheeling, West Virginia, for her question:

What is mother of pearl?

Instead of money, the early American Indians used wampum and wampum was made from mother of pearl. It is a hard, glossy material that many shellfish manufacture to line the insides of their shells. Each species uses its own recipe but most mother of pearls glow with pale moonbeam colors. Some of the loveliest are rosy pink. Wampum money beads were shaped from a patch of purple mother of pearl found inside the shell of a certain fresh water clan.

Precious pearls are made of mother of pearl, which also is called nacre. Though the lovely material glows like frozen moonbeams, it is made from very ordinary chemicals found dissolved in salt or fresh water. About 92 per cent of the basic recipe is a compound of chalky carbon. Another two per cent is plain water. The remaining six per cent is the wonder ingredient that transforms these ordinary chemicals into layers and pearly beads of nacre.

Oysters, clams and dozens of other shellfish have soft, sensitive bodies. They live inside sturdy shells that protect them from most of their hungry foes. However, their shells are made of tough material, tough enough to scratch the soft little bodies that live inside. Besides, the water that brings in food and oxygen also may bring in itchy grains of sand. Obviously, they must line the inside of their shells with something smooth and comfortable.

The something smooth is nacre. It is created by a fleshy flap called the mantle t;hich wraps around the creature's soft body like a cloak. In the mantle there is a layer of cells that rearrange the simple ingredients extracted from the water  and mixes them with a special sort of cement.

The nacre is prepared patiently, drop by gooey drop. It oozes from the nantle and spreads a thinner than thin layer on the inside of the shell or shells. The wonderful stuff dries very fast with a hard, shiny finish. This glossy paint job is hardly finished before the shellfish is ready to apply the next and then the next one.

However, the molecules are arranged in a variety of patterns. Some form smooth, shiny layers. In other layers, the fragments of nacre are arranged to act like multitudes of shiny little prisms. These prisms refract the light so that it glows like a pale pearly moonbeam.

The nacre covered walls feel comfortable. But sometimes a gritty grain of sand manages to enter and irritate the shellfish's soft little body. To solve this problem, the mantle coats it with a layer of smooth nacre. Later another smooth layer is added, then another and another and the itchy invader is encased inside a pearly bead. If the shellfish happens to be a certain species of oyster, this bead of nacre becomes a precious pearl.