Clark Melson, age 10, of San Diego, Calif., for his question:

HOW DO THEY MAKE GLASS?

Most glass is made from sandy silica, soda and lime. These main ingredients are cheap and plentiful. But the basic recipe calls for melting the mixture in a furnace at about 2,700 deg. This terrific heat uses a lot of very costly energy. What's more, the hot tacky mixture must be rolled and molded into shape and then polished. This requires a lot of highly skilled labor.

There are 100,000 recipes for making different kinds of glass. But the basic mixture is always about 72$ sand, 15$ soda and about 9% lime. A long list of other ingredients provides traces of this and that to make one type of glass different from another. Everything is melted in the fiery furnace, and some types go through more refining processes than others.