Chromium(III) oxide is an inorganic chemical compound commonly used in the upkeep of a straight razor's edge. More commonly referred to as crox, chromox or chromium oxide, chromium(III) oxide is actually one of several known oxides of the metal chromium.
Chemical composition and toxicity
Chromium(III) oxide has the empirical formula of Cr[sub]2[/sub]O[sub]3[/sub], meaning that for every two chromium atoms there are three oxygen atoms. Although this may seem to suggest that chromium(III) oxide exist as discreet molecules containing only five atoms, two of chromium and three of oxygen, this is not the case. Chromium(III) oxide is actually a large, crystalline macromolecule composed on repeating units of chromium and oxygen atoms in a ratio of 2:3.
While chromium(III) oxide contains chromium, it is relatively non-toxic. This is because chromium(III) oxide a trivalent form of chromium, meaning that each chromium atom in the compound carries a charge of +3. This distinction is important as it is hexavalent chromium, meaning that each chromium atom carries a charge of +6, that is widely known to be toxic. Although this may not seem a major difference to some, the difference is enough that it allows hexavalent chromium to easily cross cellular membranes inside the body where it is converted into trivalent chromium, accumulates and begins to disrupt cellular processes. Trivalent chromium, on the other hand, does not easily cross cellular membranes and, in small amounts, is actually an essential nutrient that helps regulate the metabolism of proteins and lipids in the body.
How to use
Chromium(III) oxide is abrasive, with a hardness of roughly 8-8.5 on the Mohs scale. To use, a thin layer is applied to either a paddle or hanging strop, and this strop is then utilized essentially like a hone. (Also see Applying paste to a strop)
In addition to its use as an abrasive, chromium(III) oxide is also a commonly used pigment in paints, inks and glasses due in part to its considerable stability. In such applications, it is known, among other names, as viridian.