zaffer

zaf·fer also zaf·fre  (zfr)

n.

An impure oxide of cobalt, used to produce a blue color in enamel and in the making of smalt.

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[Italian zaffera, from Old French safre, perhaps alteration of safir, sapphire; see sapphire, or from Arabic ufr, yellow copper, brass, from 'afar, yellow; see pr² in Semitic roots.]