Sennelier Watercolour S4 Cerulean Blue (302)

Cobalt blue is a semitransparent pigment with low to moderate tinting strength. When it dries, it appears lighter and less saturated. Pigment particles are large and grainy. Differences in how the pigment is ground and mixed lead to considerable differences in its performance among various manufacturers.

Pigment Name: PB28—Cobalt Blue

Chemical Name: cobalt(II) oxide + aluminum oxide

Permanence: Cobalt blue is absolutely lightfast and extraordinarily stable. Cobalt salts' high-temperature stability makes them the standard for blues used in ceramics and glassware.

Toxicity: Cobalt salts are toxic. Avoid respiratory and skin contact. Soluble cobalt may cause irritation and allergic reactions through contact with the skin. It is considered a possible carcinogen.

History: Since ancient times, smalt blue has been used to colour glass and ceramics. Cobalt salts, which give smalt its characteristic blue colour, were identified in the 18th century. Techniques for manufacturing Cobalt Blue, a chemically pure salt of cobalt and aluminum oxide, were developed in 1802.

Alternate Names: Smalt Blue