Cerulean Blue is similar to Azurite which was used from ancient times but lacked the high degree of permanence of the modern pigment. it is a little dark used straight from the tube for painting skies, but mixed with a little Australian Sky Blue it is often just right. Sky colors vary a great deal according to time of year or time of day, and weather is a huge factor, so no exact mixture can be given but a rule of thumb is that mixtures in varying proportions of Cerulean Blue, Australian Sky Blue, and touches of either Ultramarine Blue or Cobalt Blue will recreate the blues found in clear skies, especially in the middle part of the day.
Chemical Description: Oxides of cobalt, aluminium & chromium
Pigment Numbers: PB36
Lightfastness Rating: ASTM I
Pigment Opacity: Semi-Transparent
Paint Opacity: Semi-Transparent