borrowed from French (originally as adjective following blanc or céruse "white lead"), from litho-litho- + -pone, of uncertain meaning and origin
The word lithopone first surfaces, as far as is known, in a patent application by the Belgian pigment manufacturer François Victor Leger in 1869: "Déscription … d'une brevet d'invention pour un nouveau moyen de traiter le sulfate de baryte, afin d'obtenir un blanc, propre à la peinture, dit blanc ou céruse lithopone" ("Description … of a patent for a new means of treating the sulfate of barite in order to obtain a white pigment suitable for painting, called lithopone white [lead] or ceruse"). (For details see H. Volquartz, "Zur Frühgeschichte der Lithoponeweiss," article reprinted in the journal Fette - Seifen - Anstrichmittel, 56. Jahrgang, No. 2, 1954, pp. 123-24.) The second element of the compound has been taken as Greek pónos "labor, toil, grief," though this makes little sense. A pigment made from barium sulfate and zinc sulfide was patented in France earlier, in 1850 and 1851, by the French chemist and politician Guillaume Ferdinand de Douhet (1811-81), but de Douhet is not known to have used the word lithopone.