col·co·thar 
(kŏlkə-thər, -thär′)
(kŏlkə-thər, -thär′)n.
A brownish-red ferric oxide obtained as a residue after heating ferrous sulfate, used in glass polishing and as a pigment.
[Medieval Latin, from Spanish colcótar, from Arabic qulquṭār, possibly from Greek khalkanthos, copper sulfate : khalkos, copper + anthos, flower.]