Calx
Calx is a substance formed from an ore or mineral that has been heated.
Calx, especially of a metal, is now known as an oxide. According to the obsolete phlogiston theory, the calx was the true elemental substance, having lost its phlogiston in the process of combustion.
"Calx" is also sometimes used in older texts on artist's techniques to mean calcium oxide.Etymology
Calx is Latin for chalk or limestone, from the Greek χάλιξ. It is not to be confused with the Latin homonym meaning heelbone, which has an entirely separate derivation.
