PB28
Cobalt Blue
- Chemistry
- Cobalt aluminate
- Origin
- Synthetic mineral.
- History
- Introduced 1802 by Thénard; a clean, stable, semi-opaque blue.
- Toxicity
- Cobalt - care required.
Cobalt Blue (PB28) is Cobalt aluminate. In our watercolour range it is semi-transparent, no granulation, excellent lightfastness.
- Transparency
- Semi-Transparent
- Granulation
- NO
- Staining
- Medium
- Lightfastness
- Excellent
What is PB28?
PB28 (Cobalt Blue) is Cobalt aluminate. Synthetic mineral..
What is the chemistry of PB28?
PB28 is Cobalt aluminate.
Is PB28 toxic?
Cobalt - care required.
Is PB28 lightfast?
In the Michael Harding range, colours using PB28 are rated excellent for lightfastness.
Is PB28 transparent or opaque?
PB28 is semi-transparent.
Does PB28 granulate?
In watercolour, PB28 is non-granulating.
Which Michael Harding colours use PB28?
PB28 appears in 4 Michael Harding colours: Blue Verditer, Cobalt Blue, Cobalt Blue, Blue Verditer .
The story of PB28
A clean, reliable, mid blue - stable in all conditions, though it requires care because of its cobalt content.
How it is made
Cobalt blue is made by calcining cobalt oxide with alumina at high temperature, producing a stable crystalline pigment. Ground in oil it gives a clean, semi-opaque, slightly granular blue that dries well and is fully lightfast.
In the hands of the masters
A favourite of the Impressionists and Post-Impressionists - Monet and Renoir used it for skies and shadows where ultramarine read too warm.
Michael Harding colours using PB28
4 colours across both rangesLightfastness: Excellent
| Colour | Medium | Transparency | Lightfastness | Granulation |
|---|---|---|---|---|
| Blue Verditer No. 318 | Oil | Opaque | Excellent | — |
| Cobalt Blue No. 506 | Oil | Semi-Opaque | Excellent | — |
| Cobalt Blue W411 | Watercolour | Semi-Transparent | Excellent | NO |
| Blue Verditer W233 | Watercolour | Semi-Transparent | Excellent | YES |
Pigments in the same family
Complementary pigments to mix with PB28
Opposite-family pigments that pair cleanly with PB28 for neutrals, shadows and chromatic greys.
Open the Mixing Studio →