Manganese is a grey white metal, which has a resemblance to iron although the element is non-magnetic. Manganese ions have various colours, depending on their oxidation state, and are used industrially as pigments. Manganese dioxide (MnO2) is used to decolourise commercial glass. When added to molten glass a small amount of red-brown Mn(III) results that masks the blue-green colour from iron impurities. That is, by adding a reagent with the complementary colour of the impurity, the resultant effect is to balance out and give a clear glass.