Historically a very expensive ground lazurite pigment, synthetic pigment has been used since the 1830's making it one of the most popular and affordable blues, Yves Klein blue is mostly Ultramarine. (Series2) 

Lightfastness: I, Permanency: Excellent**, Opacity/Transparency: 6 Semi-Transparent
Pigment: Polysulfide of Sodium-Alumino-Silicate, PB29, 77007

**Not for exterior use