Transparent color originally made from ground cobalt glass and used in 16th and 17th century European paintings in place of Ultramarine. Historically Smalt loses color over time, but this modern formula offers a classic deep blue that is permanent. (Series1) 

Lightfastness: II, Permanency: Very Good, Opacity/Transparency: 6 Transparent
Pigment: Polysulfide of Sodium-Alumino-Silicate, PB29, 77007 / Carbazole Dioxazine, PV23, 51319 / Nearly Pure Amorphous Carbon, PBk7, 77266