A blue beloved of the Impressionists, it still makes appearances in the palettes of landscape painters today. It's an incredibly stable, gorgeous, useful middle-blue which is a bit more opaque than some of the other pigments.

Cobalt Blue has an interesting feel that is hard to describe, but it is helpful for portraying both solid objects and airy atmospheres. It tends to be a friendly mixer, meaning it does not overpower like some pigments do.

Cobalt Blue (Cobalt Aluminate Blue Spinel) or Thenard's Blue is one of our favorite blues and a mainstay of the palette.

This pigment was a "staple part of the Impressionist palette," along with ultramarine, according to experts on the time period. While some would prefer to mix the scale of blues using phthalo and ultramarine, we enjoy a hard-to-describe quality about cobalt related to its reflectivity.

Some list cobalt blue as semi-transparent, but we tend to think of it as semi-opaque relative to other blue pigments such as phthalo blue or ultramarine.

Cobalt blue PB28 comes in a variety of colors ranging from teal to middle blue to deep blue. Most Cobalt Blues are of the middle blue variety.

In terms of health and safety, it is listed as toxicity class B, which means it is toxic, so do use great caution. The Artist's Guide to Health and Safety has a section about some of the hazards associated with cobalt pigments. The author's most recently updated writing can be found through her site.

Cobalt Blue has historically had an excellent reputation for lightfastness.

However, some interesting quirks showed up in Golden's recent research on lightfastness, which examined different mixing white pigments in oils.

While Cobalt Blue's overally lightfastness was excellent in Titanium and Titanium Zinc Blends (ASTM I- Excellent), it showed about an ASTM II-Very Good in Lead White. A shocker was that it tanked in Zinc White. As an interesting aside, in some artificial testing methods (QUV/Xenon), the cobalts on the whole did not do well, but Cobalt Blue performed excellently in harsh Arizona sunlight exposures.

As an interesting aside, it did not do well in the Florida tests, which could suggest vulnerability to high humidity or some other factor.

Cobalt blue tends to have a very high amount of oil, and it is interesting that it still dries quickly due to the oil content, at least in linseed oil. PB28 is one of the colors which may be found in walnut or poppy oil in an effort to avoid some of linseed’s natural yellowing tendency. Some give Cobalt Blue a moderate dry time, but it does seem a bit faster than many others. Both factors -- the oil content and the drying-- are good to keep in mind if you are painting in oil and working in layers.

There are also ethical concerns with the mining of cobalt, and we urge paintmakers to find ethically mined and sourced cobalt pigments.

Cobalt does seem to have a range within the pigment code PB28 but there is also a separate pigment for Cobalt Blue Deep, PB74. Also Cobalt Chromite Blue is different, the pigment code for Cobalt Chromite is PB36.

Cobalt Aluminate Blue has a reflectance in the near-infrared, making it a cool pigment. One sometimes hears about spinel colors and it was interesting to find out that PB28 also has a spinel structure.

There is a fairly rare turquoise version of PB28. Usually we'd associate a color like this with related cobalt pigments such as PG50. PB28 can be found in shades ranging from dark blue, to mid blue, to light greenish blue.

We've found several versions of the elusive PB28 Turquoise version. Vasari makes a fairly famous Cobalt Turquoise beloved by painters, but we were also delighted to find a PB28 turquoise from RGH.

Cobalt Blue had a beloved place on the palettes of historical painters and may be worth trying, especially for landscape and realist paintings.