Rublev Colours Pigment Cobalt Chromite Blue - 100 g

Cobalt Chromite Blue pigment is cobalt chromite blue-green spinel (Co[Al,Cr]₂O₄). It is a deep blue-green powder produced by solid-state reactions at a very high temperature. It is lightfast, alkali, acid, heat, and weather resistant. It was created to color concrete, stucco, and grout but is excellent in artists' painting mediums. It is also compatible with ceramic bodies and low zinc glazes.

Cobalt Chromite Blue is made by calcining at 2400°F a mixture of cobalt (II) oxide, chromium (III) oxide, and aluminum (III) oxide in varied ratios, forming an interdiffused crystalline spinel matrix. Its constitution may also include one or more modifiers, zinc oxide (ZnO), manganese oxide (MgO), silicon dioxide (SiO₂), titanium dioxide (TiO₂), or zirconium dioxide (ZrO₂) to adjust color hue or other properties. 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.

Cobalt chromite blue pigment has good ultraviolet and visible light opacity and is chemically inert, heat resistant, and stable to ultraviolet light. It is non-bleeding and non-migratory. It has exceptional durability and hiding power and is generally used in applications where resistance to heat, light, and weather is needed. It is compatible with most resins and polymers and is non-warping. Typical applications (noninclusive) are liquid and powder coatings, inks, dispersions, concrete, plastics, and other applications where equivalent pigment chemistry is used.

This pigment is easily dispersed, does not need grinding, and can be stirred using most laboratory and production equipment to achieve complete dispersion.

Water-Based Paint

Cobalt chromite blue is a semi-transparent pigment with moderate tinting strength in most water-based paints. 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

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

Oil Absorption and Grinding

Cobalt chromite blue absorbs a moderately high amount of oil, about 17 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 about 80 percent dry pigment to 20 percent by weight of poppy seed or walnut oil, either of which some artists prefer to linseed oil. Cobalt chromite blue has a greenish tone that is more or less reddish blue when viewed under incandescent light.

Toxicity

Cobalt chromite blue is not considered toxic; however, care should be taken when 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 skin and mucous membranes. No statistically significant results were found in studies on rats to determine the carcinogenic potential. Soluble cobalt compounds and cobalt metals may have a sensitizing effect. However, none have been reported during many years of handling cobalt blue pigments.