John Sanborn, age 12, of Milwaukee, Wis., for his question:

WHAT ARE TESSERAE?

A mosaic is a beautiful decoration made by fitting small pieces of colored glass, stone or other material together. The pieces are set in a type of cement to form a pattern on some surface. A mosaic is usually a picture on a wall, ceiling or floor. The colored pieces of material used to make the mosaic are called tesserae. A single piece is called a tessera.

Colored tesserae are generally tile or marble if the mosaic is going to be used on the floor and generally colored glass or pebbles if the design is going to be used on the wall.

Mosaics were used by Greek, Roman and early Christian artists. They are also found in ancient Byzantine. buildings. The Indians of Latin America were also known for their fine examples of mosaic work.