Larry Anderson, age 9, of Des Moines, Iowa, or his question:

What is indigo?

Indigo is a color the deep, rich blue in the peacocks tail, the lustrous blue of lapis lazuli. In the rainbow it is the radiant band of color between lighter blue and violet and, in the desert on a hot clear day, the sky directly overhead may be indigo blue. This lovely color has always been one of man's favorites. He learned to steal it from certain plants before the dawn of history. He used it to dye his clothes and even his skin.

Indigo dye can be extracted from several plants of the pea family‑ you cannot see the blue in the plants or their flowers. It is a chemical, a compound of carbon, hydrogen, nitrogen and oxygen. Growing the plants and extracting the dye is a long and costly process and, about 80 years ago, chemists learned to make the dye synthetically. Most of our indigo dye is now man‑made and the bushy little indigo plants have been, you might say, put out to pasture.

Until the Age of Science, however, indigo was a valuable, world‑wide crop. The Chinese used one plant, the Indians of Bengal another. The Celts of ancient Britain got indigo from a plant named weed. Before the days of Caesar the warrior Celts dyed their skins with this welled indigo.

Vegetable indigo is still used where a strong, permanent dye is needed. Most of the supply is produced in Bengal, though China, Ceylonl, Mexico and Java still produce small indigo crops and extract the dye. The indigo seeds are sown in the spring. The first crop is all ready three months later. The plants are bushes about three feet tall and decked with flowers like small, deep pink sweat peas. There is no glimpse of the lovely blue dye. The plants are cut and immediately crushed and soaked in water. After a while a second crop and, maybe, a third will grow from the cut stubs.

The harvested indigo plants, stems, leaves and blossoms, are soaked from nine to 14 hours. Bacteria and chemicals in the plants cause the fermentation. The liquid turns a clear yellow. The plants are removed and the liquid is stirred. This brings it into contact with oxygen in the air. Oxidation causes blue flakes to form. At last, we see the blue dye. The liquid is drawn off and the blue flakes dried and pressed into cakes.

This is how, from earliest times, man got his blue dyes. In 1880 a German chemist named Adolf Von Baeyor made synthetic indigo from coal tar. This man‑made dye was as useful as the natural vegetable indigo. But, the process of making it was expensive. It cost more than natural indigos.

However, industry decided that Adolf was on the right track. Coal tar is cheap. What was needed was a simple, inexpensive method to make indigo from this cheap raw material. This required money and research. Many scientists worked on the job for a job that took 1? years and five million dollars. When it was done they had a simple indigo dye; for most purposes as good as natural indigo and at less than half the cost.