Cerulean blue

Cerulean blue is a synthetic inorganic pigment powder, cobalt(II) stannate (Co₂SnO₄, PB35): genuine cerulean, a clear sky blue with a slight green tone. It is opaque, lightfast and stable to alkalis, lime and weather, and is used in oil, acrylic, tempera, watercolor, gouache and fresco, above all for skies.

Key facts

• Color: clear sky blue with a slight green tone
• Pigment type: Synthetic inorganic pigment (cobalt stannate)
• Colour Index: PB35 (C.I. 77368)
• Composition: cobalt(II) stannate, Co₂SnO₄, with small amounts of magnesium and aluminum oxides (supplier data)
• Origin: synthetic
• Also known as: coeruleum, Höpfner blue
• Opacity: opaque
• Lightfastness: 8 of 8 on the Blue Wool Scale (supplier data)
• Chemical resistance: alkali 5/5, lime 5/5, acid 5/5 (supplier data, 5 = best)
• Suitable for: oil, acrylic, egg tempera, watercolor, gouache, fresco (lime), lime and cement plaster
• Packaging: 25 g jar · 1 kg bag

How to use

Mull it with a muller or palette knife into linseed oil, gum arabic, egg yolk or acrylic medium. Cerulean has very low tinting strength but covers well, so it is used mostly on its own or with white for skies and cool light blues rather than as a strong mixing color. In watercolor it can look slightly chalky, which it loses in oil; some painters bind it in poppy oil to keep the blue clean. It is lime-proof and suits fresco, silicate binders and concrete.

About cerulean blue

Cobalt stannate was first made around 1800 (sources give 1789 and 1805) and became known as Höpfner blue. It entered artists' palettes in the second half of the 19th century, when British colormen sold it as "coeruleum", from the Latin caeruleus, "blue", related to caelum, "sky". It was used mainly for painting skies.

Safety

Contains cobalt compounds: may cause allergic skin or respiratory reactions; harmful if inhaled. Handle dry pigment with care: avoid breathing the dust and contact with eyes. Wear a dust mask (FFP2/N95) and gloves when working with the powder, work in a well-ventilated area and wipe up spills with a damp cloth. Do not eat, drink or smoke while working; wash your hands afterwards. Keep away from children and pets. For artistic and technical use only — not for cosmetics, food or tattoos.

FAQ

Is this genuine cerulean blue?

Yes. According to our supplier it is cobalt stannate, PB35. Some paints sold as cerulean contain cobalt chromite, PB36, instead; we sell that pigment separately as Cobalt Chrome Sea Wave.

How does Cerulean blue differ from Cerulean blue dark?

Both are sold by our supplier as cobalt stannate (PB35) with the same test data. Cerulean blue is the lighter sky blue; Cerulean blue dark is a deeper azure.

Can cerulean be used in fresco?

Yes. It is lime-proof (supplier data: lime 5/5) and suits fresco and other lime techniques.