Chrome Oxide

Alternate Names: Chromium (III) Oxide, Cr₂O₃, Chromium Oxide

Oxide	Analysis	Formula
Cr2O3	131.58%	1.00
Oxide Weight		152.00
Formula Weight		152.00

Notes

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.

Chrome is refractory on its own (as are chrome containing materials like Chromite). It is used to make refractories. One supplier, termorefractories.com, says: "Chrome magnesite refractory bricks are produced from sintered magnesia and chrome ore that has refractory level. Content of chrome-magnesite refractory bricks is generally, 15-35% Cr₂O₃ and 42-50% MgO whereas magnesite-chromite refractories contain at least 60% MgO and 8-18% Cr₂O₃. Bonding space between refractory grains is done with silicate."

Related Information

How do metal oxides compare in their degrees of melting?

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.

Chrome oxide original container bag

Links

Temperatures	Chrome oxide decomposes (990-)
Temperatures	Chrome oxide melts (1990-)
Materials	Chromium Trioxide
Hazards	Chromium Compounds Toxicology
Typecodes	Generic Material Generic materials are those with no brand name. Normally they are theoretical, the chemistry portrays what a specimen would be if it had no contamination. Generic materials are helpful in educational situations where students need to study material theory (later they graduate to dealing with real world materials). They are also helpful where the chemistry of an actual material is not known. Often the accuracy of calculations is sufficient using generic materials.
Typecodes	Colorant Metallic based materials that impart fired color to glazes and bodies.
Oxides	Cr2O3 - Chrome Oxide
Glossary	Metal Oxides Metal oxide powders are used in ceramics to produce color. But a life time is not enough to study the complexities of their use and potential in glazes, engobes, bodies and enamels.

Data

Frit Softening Point	1990C M
Density (Specific Gravity)	5.21

By Tony Hansen
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