What is a deep blue pigment or coloring material used in various arts. It is a vitreous substance made of cobalt, potash, and calcined quartz fused, and reduced to a powder called?

smalt — A deep blue pigment or coloring material used in various arts. It is a vitreous substance made of cobalt, potash, and calcined quartz fused, and reduced to a powder. (Webster's 1913.)

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