Cobalt Blue

Artificial inorganic pigment

Pigments sorted by Colour | Type | First date of use | Elements | Pigment timelines

Composition and Properties of Cobalt Blue

Cobalt blue (Thénard’s blue) is a mixed oxide of cobalt and aluminum CoO • Al₂O₃. It can also be considered to be cobalt (II)-aluminate with the formula of CoAl₂O₄.

It is very stable and is unaffected by heating and by concentrated acids and alkalis. The pigment is practically unaffected by light and is compatible with all other pigments.

Art Teachers' Materials

Richly illustrated presentation on the properties, preparation, identification and use of this pigment

Pigment

Painted swatch

Image courtesy of Technisches Museum Wien

Names of Cobalt Blue

Alternative names

Thénard’s blue

Color Index

PB 28, CI 77346

Word origin

From the German word Kobold meaning evil house spirit. The name was originated by medieval miners who believed, that cobalt ores made it difficult to extract silver from silver ore.

Kobaltblau

German

bleu de cobalt

French

Azzurro di cobalto

Italian

Azul de cobalto

Spanish

Preparation of Cobalt Blue

Attention: Cobalt compounds are highly toxic and should not be handled by people not trained to do so.

Cobalt blue can be prepared by heating a mixture of cobalt (II)-chloride CoCl₂· 6H₂O and aluminum oxide Al₂O₃.

The mixture of cobalt (II)-chloride and aluminum oxide is first homogenized in a mortar.

The mixture is then heated in a test tube with the aid of a Bunsen burner for several minutes.

The resulting mass of cobalt blue is finely pulverized in a mortar.

Video: 'Cobalt Blue Part 1' by The Alchemical Arts

Video by The Alchemical Arts

References

References

(1) Citoyen Thénard, Considérations générales sur les couleurs, suivies d’un procédé pour préparer une couleur bleue aussi belle que l’outremer, Journal des Mines 86: 128–136 (pdf of the original article by Thénard)

(2) Gehlen, A.F. (1803). “Ueber die Bereitung einer blauen Farbe aus Kobalt, die eben so schön ist wie Ultramarin. Vom Bürger Thenard“. Neues allgemeines Journal der Chemie, Band 2 (H. Frölich.). German translation from Thénard, L.J. (1803, (Brumaire, XII)) (pdf of the translation of the original article by Thénard into German).

History of Use

Cobalt blue has been used since its first preparation by Thénard in 1803-04 and it is still one of the most popular blue pigments. The following graph gives the frequency of its use in the paintings of the Schack Collection in the Bavarian State Art Collections in Munich (1).

An extensive collection of occurrences of this pigment in paintings from several historical periods can be found in the blog post ‘Pigment: Cobalt Blue, the 19th-century sky‘ by The Eclectic Light Company.

References

(1) Kühn, H., Die Pigmente in den Gemälden der Schack-Galerie, in: Bayerische Staatsgemäldesammlungen (Ed.) Schack-Galerie (Gemäldekataloge Bd. II), München 1969.

Examples of use

William Turner, The Fighting Téméraire tugged to her last berth to be broken, 1838

Pierre-Auguste Renoir, The Umbrellas, 1880-86

The clothes of the mother and her daughters on the right are painted in cobalt blue, while the grey-blue dress of the woman in the left part of the image contains artificial ultramarine.