Gary Vancil, age 11, of Selma, Alabama, for his question:

How do they make a mirror

A mirror has a shiny surface and a dark backing. The light that strikes the surface is stopped from passing through the glass and forced to turn around and reflect back, somewhat like a bouncing ball. Mirrors can be made from all kinds of shiny surfaces. But a good mirror is an expert job of craftsmanship. The sheet of heavy glass must be crystal clear and without bumps or blemishes. It must be cleaned and polished to perfection.

The backing is a series of thin, smooth coatings, each applied with care and accuracy. The base coat is a tissue thin layer of tin chloride. When rinsed and dried, a watery solution of silver salt is applied drop by drop. In about one minute, individual particles of silver stick to the base coat, forming a second coating. The mirror is tenderly taken to an electrolytic bath for the next operation. This deposits the third layer of copper particles. The copper is coated with lacquer and finally a coat of dark paint is added to complete the mirror backing.