Rublev Colours Dry Pigments - Series 5 Cobalt Aluminate Blue is a premium, modern inorganic cobalt blue spinel pigment prized for extreme permanence, clean colour, and industrial-grade stability. Made from cobalt aluminate blue spinel (CoAl2O4) and produced by high-temperature calcination, this deep blue powder forms a durable crystalline spinel matrix that is chemically inert, non-bleeding, non-migratory, and highly resistant to heat, light, and weather.

Known as Pigment Blue 28 (PB 28), Cobalt Aluminate Blue is one of the most durable blue pigments commercially available. It offers strong UV and visible opacity and excellent hiding power in demanding applications. Artists and makers choose it when they need long-term colour stability in studio and workshop use, including paint making, inks, dispersions, coatings, plastics, and other resin systems where equivalent pigment chemistry is used.

This pigment is also valued for practicality: it is easy to disperse and typically does not require grinding, allowing you to achieve an even dispersion with standard mixing equipment. In water-based systems it can appear lighter and less saturated once dry, and in watercolour it may show a characteristic granulation due to natural flocculation, which many artists actively seek for texture.

Key specs

• Colour Index: PB 28 (77343)

• Pigment type: Synthetic inorganic

• Chemical formula: CoAl2O4 (cobalt aluminate blue spinel)

• ASTM lightfastness: I (Acrylic, Oil, Watercolour)

• Mean particle size: 1.2 micrometers

• Heat stability: up to 800 C

• Oil absorption: 34 g oil / 100 g pigment

• Series: 5

• Size: 100g

Handling and safety
No acute or known chronic health hazards are associated with anticipated use, but as with all dry pigments avoid inhaling dust and avoid ingestion or prolonged skin contact. Conforms to ASTM D-4236.