Richard Post, age 15, of Houston, Texas, for his question:

How do they color glass?

In the past, glass makers kept their recipes secret. For example, the artisans of Venice accidentally discovered that a trace of copper added to the molten brew created glass of a rich ruby red. Nobody dared to divulge this secret because the sale of this gorgeous glass brought wealth to the city. Artisans throughout the civilized world knew how to make glass from a basic brew of sand, lime and soda. Some discovered that extra ingredients added jewel tone colors. But the Venetian recipe remained a secret for centuries.

Nowadays we know dozens of different ways to color glass    and new methods are discovered constantly. As in the past, the colors are added by extra ingredients in the basic molten recipe. A trace or two of nickel imparts a range of colors from sunbeam yellow to rich amethyst. Traces of cobalt create glassy blues. Copper still imparts red and a small helping of gold gives a different red. A modern glass factory has thousands of recipes with dozens of different chemicals capable of freezing the colors of the rainbow in glittering crystal.