Cobalt Blue (No. 506)
Inorganic
| Colour Index | PB 28 |
| Drying Speed | Very Fast |
| Opacity Covering and Tint Power | Semi-Opaque |
| Lightfastness | Excellent |
| Oil Content | Average, Linseed |
| Toxic | No |
| Conforms To | ASTM D-4236 |
Introduced at about the same time as Ultramarine, Cobalt Aluminate is a synthetic inorganic pigment. It is a more greenish blue, with a heavier, more mineral appearance when seen as dry pigment. The hues formed from it are correspondingly heavier and greyer. But it has a certain shade which the less expensive ultramarine cannot quite match. The paint film when cured is quite soft.