Deborah weeks, age 12, of Shreveport, La., for her question:

What is lac?

The first car owners needed a month or more to paint up their buggies. Nowadays, the job is done in a few hours. The speed up began in the 1920s when lac substances replaced ordinary paint as car finishes. Since that time a vast array of these fast drying, glossy coats have been developed, and our clever chemists are improving them constantly.

The word lac is related to shellac and to lacquer. All these words stem from a Persian word meaning 100,000. This vast number refers to a swarm of tiny scale insects native to India and other warm lands of the east and Middle East. Most of these little flat bugs measure about one-fortieth of an inch, and one of their favorite homes is the tender shoot of a fig tree.

The lac insects feed on plant sap and use their long hard beaks to burrow through the tree bark and suck up the sweet juices from the living wood. Hundreds or thousands of the little bugs may crowd together on a single twig. As they digest the sap, they transform certain resins into a tacky gum, which oozes through their bodies. The clustering brood becomes covered with a scaly coating, which is why they and many insects like them are called scale insects. The hard, gummy coating serves as armor to protect them from hungry enemies.

Since ancient times, the scale encrusted twigs have been gathered and processed to separate the gummy lac from fragments of wood, bugs and other debris. In the past, quantities of the lac were used to make sealing wax and other molded plastics. Later, most of it became shellac for making electric insulators and phonograph records, varnishes and a host of glossy finishes.

The scale insects manufacture their lac from plant resins. In ancient China, glossy lacquers were made directly from the gooey resins of certain Evergreens. We use lac from both the lac insects and plant resins to make our wonderful assortment of hard, fast drying lacquers. Our lacquers, or lac spreads, are liquids containing dissolved cellulose and complex plant chemicals called epoxies, urethanes and acrylics. Nowadays, we find these chemical terms on our wonderful, up to date glues and spray cans.

Ordinary paints and enamels become hard and dry because of chemical changes that take place within the mixtures. Lac substances dry because the liquid in which the chemicals are dissolved evaporates. When the manufacturers create a fast drying lacquer, they dissolve the resinous lac chemicals in a volatile solvent. Some of these fast drying liquids evaporate in minutes, leaving the car, the furniture or the floor coated with a hard, glossy finish.