In alchemy, chalcanthum, also called chalcanth or calcanthum, was a term used for the compound blue vitriol (CuSO₄), and the ink made from it. The term was also applied to red vitriol (a native sulfate of cobalt), and to green vitriol (ferrous sulfate).

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Some maintained calcanthum to be the same thing as colcothar, while others believed it was simply vitriol (sulfuric acid).^{[citation needed]}

1.  This article incorporates text from a publication now in the public domain: Chambers, Ephraim, ed. (1728). "Chalcanthum". Cyclopædia, or an Universal Dictionary of Arts and Sciences (1st ed.). James and John Knapton, et al.
2. Webster's Revised Unabridged Dictionary (1913)