Lac, a resinous substance produced by the lac insect and used to make shellac. Shellac is used as a finish and in making lacquer and polishes. It is also used to stiffen felt hats and as an electrical insulator.

The tiny lac insects infest trees and shrubs in India and Southeast Asia in vast numbers. (Their name comes from the Hindi lakh, meaning “hundred thousand.”) As the insects pierce the thin bark of twigs and feed on plant sap, they give off a red liquid that dries to form lac. The lac provides a protective cover under which each insect lays its eggs and then dies. The young scramble out to infest adjacent twigs, beginning the cycle anew.

In spring and fall workers cut the infested twigs, called stick lac, and fasten some to other plants on which they wish the insects to breed. The remainder they crush, wash, and filter to form seed lac. This is placed in a long cotton tube and heated before a fire. As the lac melts, the tube is twisted to squeeze it out.

The collected lac is spread out into thin layers and allowed to dry into sheets. The sheets are broken up into flakes, thus forming the shellac commonly used in commerce. (Liquid shellac is made by dissolving these flakes in alcohol.) Shellac is orange-red in color. It becomes transparent when bleached with chlorine. Most of the world's shellac production comes from India.

Lac may also be formed into cakes instead of sheets. The cakes are called button lac or garnet lac.

The lac insect is Laccifer lacca of the superfamily Coccoidea of the order Homoptera. It is one of a group of insects called scale insects.