Lucille Moun, age 11, of St. Catharines, Ontario, for her question:

How do they make a mirror?

In ancient times, the ladies primped in front of mirrors made of metal. Such a mirror might be made of gold, silver or bronze, and only the rich could afford one. The mirror side of the metal was polished to a high finish, and the back was often etched with designs.

It was not always safe to tell the secrets of mirror making. In the 16th century, the best glass mirrors were made in Venice and the manufacturers had strict laws to protect , their secrets. If anyone told these trade secret, he could be executed. If he escaped from Venice, his nearest relatives were imprisoned.

Times have changed and nowadays, anyone can make a mirror. All you need is a glossy surface to reflect back the light. The best mirrors are made of shiny glass backed with silver to stop the light frown passing through and make it bounce back a reflection. This sounds easy but the job calls for delicate precision and good mirrors are made only by experts.

A mirror maker uses clear and sturdy plate glass, free from flaws and polished to a shiny finish. It is backed with silver, but this delicate job is done in a round about way. The glass is first coated with a layer of tin chloride and rinsed to remove the loose particles. Next a solution of silver salts is applied. The tin chloride reacts by pulling out the silver atoms from the solution and sticking them to the glass.

This chemical reaction takes but a few minutes. Then the mirror is rinsed again to remove surplus particles, for the layer of silver must be thinner than thin. The mirror is now ready to reflect a ciear image, but the thin and level layer of silver needs another coat to protect it. As a rule, it is coated with copper and the job is done by electroplating.