is a residual substance, sometimes in the form of a fine powder,
that is left when a metal combusts or is calcinated due to heat.
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. Calx is the Latin for
heel : the tarsus Calx is also the Latin base for lime and to
tread. 2008, Oxford Pocket Dictionary, Oxford University Press:
Oxford, UK.. In Popular Culture - UK Electronic music artist,
Aphex Twin (Richard David James) named some of his tracks after
different coloured Calx (green, yellow and blue).