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Reference.org
Calx
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<p>Calx is a substance formed from an ore or mineral that has been heated. Calx, especially of a metal, is now understood to be an <a href="/facts/Oxide/DXtoVe1C">oxide</a>. The term is also sometimes used in older texts on artists' techniques to mean <a href="/facts/Calcium_oxide/Wh9C8l7j">calcium oxide</a>. </p><p>According to the obsolete <a href="/facts/Phlogiston_theory/6PDveBmv">phlogiston theory</a>, the calx was the true elemental substance that was left after phlogiston was driven out of it in the process of <a href="/facts/Combustion/ohQoWj8z">combustion</a>. </p>