Words related to lac
also shell lac, "lac melted and formed into thin plates," 1713, from shell (n.) + lac; so called for its form. It translates French laque en écailles "lac in thin plates." Commercially, lac came as stick lac (still on the twigs, insects and all), seed-lac (resin without the twigs and insects, partly processed), and fully processed plates of shell lac.
The dye is obtained from certain lichens. It is naturally blue but turns red in acid and is restored to blue by alkalis. Figurative use of litmus test is first attested 1957, from scientific use of litmus-treated paper as a chemical indicator. Litmus paper with this meaning is from 1803.