What is cobalt blue?

Cobalt Blue

Cobalt blue is a vibrant blue pigment made by sintering cobalt(II) oxide with alumina (aluminum oxide) at high temperatures.

• Composition and Manufacture: The chemical formula for cobalt blue is typically CoAl₂O₄. It is a spinel-type structure. The intensity of the blue color is dependent on the proportion of cobalt present.

• Properties: Cobalt blue is valued for its:

  • Excellent lightfastness (resistance to fading)
  • Chemical stability
  • Insolubility in water and alkali
  • Good hiding power (opacity)
  • Relatively non-toxic compared to other historical blue pigments.

• History: Discovered in 1802 by Louis Jacques Thénard, it offered an alternative to the expensive and sometimes unstable ultramarine (lapis lazuli) and other cobalt-based pigments like smalt.

• Uses: Cobalt blue has been used in a wide variety of applications, including:

  • Fine art paints (oil, acrylic, watercolor)
  • Ceramics
  • Glassmaking
  • Plastics
  • Cosmetics (though restricted in some regions)
  • Printing inks

• Variations: There are subtle variations in cobalt blue depending on the manufacturing process and other additives. For example, cerulean%20blue is another distinct blue pigment based on cobalt.

• Toxicity: While less toxic than some historical pigments, cobalt compounds can still be harmful if ingested or inhaled in large quantities. Proper handling and safety precautions are advised.