Have any idea what makes the mirror work, the one that you take for granted and look into several times a day, being as vain as you are? For thousands of years, the only mirrors used by man were made of polished metal -- brass, bronze, silver or gold. In about 1300, the craftsmen in Venice discovered a way of making mirrors of glass by backing them with a coating of mercury and tin. Very soon, these glass mirrors took the place of metal ones. But even the glass mirrors were far from perfect. In 1961 somewhere in France, a way of making plate glass was discovered. Because plate glass has more weight and brilliance, it is much more suited to mirrors then ordinary glass. The next great step forward was the use of a thin silver-lining coating on the back of a mirror - instead of the tin-mercury mixture. Not only were the mercury fumes dangerous to the workmen, but the new silver coating reflected more rays of light and made better mirrors. It also led to speeding up the process of manufacturing as well as made mirrors less expensive. Today, plate glass 1/4 inch in thickness is used in making the best grade mirrors. The glass is first cut to the desired size with a diamond cutter. In the 'roughing mill', the edges are treated with sand and water. It is next smoothed with fine sandstone and polished with rouge-covered felt buffers. Before silvering, a thorough cleansing takes place to insure clearness. Gotta let all that beauty shine through, reflecting greatness! The glass is then placed on a warm, padded table. Over it is poured a mixture of ammonia, tartaric acid, and nitrate of silver. This readily sticks to the glass because of the heat. Then the silver is protected with a coat of shellac, and an application of paint which is free from any oils or acids that would injure the silver. Today, of course, mirrors are used by dentists to let them look into hard-to-se places. Mirrors are a vital part of the periscopes of submarines. The image striking one mirror in a tube is sent down the tube to the other mirror into which the observer is looking.. Mirrors are used in other ways too: in telescopes, in flashlights, in searchlights, in headlights of automobiles, and in lamps in lighthouses. In most of these, however, the curved reflector (or mirror) is usually of a highly polished metal that concentrates the light and throws it ahead.