Alternate Names: Chromium (III) Oxide, Cr2O3, Chromium Oxide
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|DENS - Density (Specific Gravity)||5.21|
|GSPT - Frit Softening Point||1990C M|
Chrome oxide is a very refractory ceramic colorant (even a 50% mix with a high borax frit will not even begin to melt it in a crucible). Chrome oxide is the only stable oxide of the metal chromium. It is a bright to dark green crystalline powder insoluble in alkalis and acids. It is manufactured from the mineral Chromite mined in southern Africa, Asia, Turkey and Cuba. As with other powerful coloring agents, chrome must be milled fine enough to eliminate specking in glass or glaze.
Chromium is a 'fast' colorant, meaning can produce strong green colors under all furnace conditions, slow or fast, reducing or oxidizing. It is also a flat colorant (due to its refractory nature), it usually produces an army helmet opaque green. It is powerful, typically only 2% will produce a dark color. It cannot be used to make a metallic glaze.
Chrome oxide is usually employed in raw glazes whereas potassium dichromate is used in fritted glazes.
Since Cr2O3 becomes 2CrO3, oxygen is captured from the surroundings, thus the percentage (or conversion factor) is greater than 100.
Metallic oxides with 50% Ferro frit 3134 in crucibles at cone 6ox. Chrome and rutile have not melted, copper and cobalt are extremely active melters. Cobalt and copper have crystallized during cooling, manganese has formed an iridescent glass.
Out Bound Links
The dangers of these materials in the ceramic process and industry
In Bound Links
Chromium (VI) Oxide, CrO3
Between the melting and boiling points (and, of course, especially while boiling is proceeding) all glaze compounds vaporize to some extent. The amount of vaporization is related to the time and temperature and atmosphere of the firing. Obvious examples of cases where vaporization must be considered...