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.
Pigment Classification: Inorganic Color Index Name: PB29 Color Index Number: 77007 Chemical Description: Polysulfide of Sodium-Alumino-Silicate Opacity/Transparency: Semi-Transparent Lightfastness Rating: 1 Permanency: Not for Exterior Use Munsell Notation Listing: N/A Gloss Average: N/A Viscosity Range: 75-100 CPS CIE L*a*b* Values: N/A Tint Strength: N/A