zaffer

American  

[zaf-er] / ˈzæf ər /

Or zaffre

noun

1. an artificial mixture, resembling smalt, containing cobalt oxide and, usually, silica, used to produce a blue color in glass and in ceramic glazes.

---

zaffer British  

/ ˈzæfə /

noun

1. impure cobalt oxide, used to impart a blue colour to enamels

---

Etymology

Origin of zaffer

1655–65; < Italian zaffera, perhaps < Latin sapphīra sapphire