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Chromium(III) Oxide (Cr2O3)

Chromium(III) oxide (or chromia) is an inorganic compound with the formula Cr2O3. It is one of the principal oxides of chromium and is used as a pigment. In nature, it occurs as the rare mineral eskolaite.

Because of its considerable stability, chromia is a commonly used pigment. It was originally called viridian. It is used in paints, inks, and glasses. It is the colorant in "chrome green" and "institutional green."

Amphoteric chrome oxide is the only stable oxide of chromium metal and can be used at all temperatures to 1200°C. This leaves a margin before it begins to volatilize around 1240°C, the fumes are very toxic.

Chromium is a 'fast' color, meaning it produces its characteristic green in slow or fast and oxidizing or reducing firing. It is also used in paints and dyes. The green color produced by chrome only is generally a drab army-helmet green.

Chromium is used in the glass industry to make green glass (up to 1%). Antimony is sometimes used as a reducing agent to ensure an emerald green.

Chromium is not very soluble in glass and does not form silicates or combine with fluxes readily unless compounds are finely ground (e.g. ball milled) and dispersed and amounts are not excessive (1% will dissolve in most glazes and give good color, but amounts above that are increasingly likely to opacify the glass rather than color it more, this is happening because it is not dissolving in the melt). Amounts up to 3% in a glaze recipe gives greyish green coloration.