Cerulean Blue Pigment

Rublev Colours Cerulean Blue pigment is composed of cobalt stannate. Cerulean blue is made by roasting cobalt and tin oxides. Cobalt blue pigments are the most durable blue pigments commercially available. They have excellent chemical and heat stability and can be used in chemically aggressive environments and exterior durable applications without color fade.

This pigment is very easily dispersible, does not need grinding for dispersion, and can simply be stirred using most laboratory and production equipment to achieve full dispersion.

For a detailed explanation of the terms in the table above, please visit Composition and Permanence.

Origin and History

The name “Cerulean blue” comes from Latin caeruleus meaning dark blue caelum which in turn probably derives from caelulum, diminutive of caelum, “heaven, sky”.

Cerulean blue is cobalt stannate that was introduced as a pigment in the 1860s. Very stable and lightfast greenish-blue with limited hiding power. Cerulean blue has a fairly true blue (not greenish or purplish) but it doesn't have the opacity or richness of cobalt blue. It was not recommended for use in watercolor painting because of chalkiness in washes. In oil, it was particularly valuable to landscape painters for skies.

The compound was known from the early 19th century, but was first introduced as an artist’s pigment by George Rowney: Gettens and Stout say that date was 1860, but Mayer gives it as 1870 (Mayer, R. The Artists Handbook of Materials and Techniques Edit. Smith, Edwin 3rd ed 1973, p. 46). In 1887 the author of a Winsor and Newton publication was hardly enthusiastic about the pigment. He comments, “By daylight it is a light greenish-grey blue with little depth or richness of colour. Unless used with care it is apt to produce a chalky effect, and it washes in a very indifferent manner” (Taylor, J. Scott, Modern Water-Colour Pigments 1887, p. 58). Cerulean blue is used in both oil and watercolor, it covers well but is not strongly staining. It suffers less from metameric effects than the other cobalt blues.

Source

Cerulean blue or cobalt tin blue (CoO.nSnO₂) is an inorganic pigment that is the reaction product of calcining a mixture of different amounts of both cobalt (II) oxide and tin (III) oxide. They are homogeneously, ionically entwined forming a crystalline spinel-type matrix. The constitution may additionally have Al₂O₃, Fe₂O₃, and/or NiO as modifiers that are used to adjust color hue and other properties that may be needed in specific applications. Cerulean blue is cobaltous stannate and is made by mixing cobaltous chloride with potassium stannate. The mixture is thoroughly washed, mixed with silica and calcium sulfate, and heated.

Permanence and Compatibility

All cobalt blue pigments are chemically inert, absolutely insoluble, have good hiding power and excellent heat stability, and show very good lightfastness and weather resistance.

Water-Based Paint

In most water-based paint, Cerulean blue is a semi-transparent pigment with moderate tinting strength. When it dries, it appears lighter and less saturated. Although pigment particles are very fine, they flocculate, giving a grainy appearance in watercolor. Differences in how the pigment is ground and mixed lead to considerable differences in its performance.

Oil-Based Paint

In oil-based paint, Cerulean blue is a semi-transparent pigment with moderate tinting strength. Differences in how the pigment is ground and mixed can lead to considerable differences in its appearance.

Oil Absorption and Grinding

Cerulean blue absorbs a moderately high amount of oil; about 55 grams of linseed oil per 100 grams of pigment to make a paste. It has been noted in some manuals that the pigment works better as a watercolor than it does in oil, and is highly valued on that account among moist colors used by artists. Grinding it for artists' use in oil will require 35 percent dry pigment to 65 percent by weight of poppy seed or walnut oil, either of which is preferred by some artists to linseed oil. Cerulean blue has a neutral blue hue that when viewed under incandescent light is more or less greenish-blue.

Toxicity

Cerulean blue is not considered toxic, however, care should be used in handling the dry powder pigment to avoid inhaling the dust. All toxicological studies showed no signs of toxicity to humans or the environment.

In animal studies, cobalt blue pigments did not display acute toxicity. No acute irritant effect was shown in tests to determine the acute irritation of the skin and mucous membranes. In studies on rats to determine the carcinogenic potential, no statistically significant results were found. Soluble cobalt compounds, as well as cobalt metal, may have a sensitizing effect. However, none have been reported during the experience of many years of handling cobalt blue pigments.

Ecology

Since cobalt blue pigments are inert and practically insoluble in water, they do not pose a hazard to the environment. The pigment can be removed mechanically from effluents. On controlled dumpsites, no dissolved heavy metals are released into the seepage water.

For more information on how to handle pigments safely, please visit How to Safely Handle Art Materials and Pigments.