Editing Portland cement (section)

===White portland cement===
[[White portland cement]] or white ordinary portland cement (WOPC) is similar to ordinary grey portland cement in all respects, except for its high degree of whiteness. Obtaining this colour requires raw materials with lower low Fe<sub>2</sub>O<sub>3</sub> content, and some modification to the method of manufacture, among others a higher kiln temperature required to sinter the clinker in the absence of ferric oxides acting as a flux in normal clinker. As Fe<sub>2</sub>O<sub>3</sub> contributes to decrease the melting point of the clinker (normally 1450&nbsp;°C), the white cement requires a higher sintering temperature (around 1600&nbsp;°C). Because of this, it is somewhat more expensive than the grey product. The main requirement is to have a low iron content which should be less than 0.5&nbsp;wt.% expressed as Fe<sub>2</sub>O<sub>3</sub> for white cement, and less than 0.9&nbsp;wt.% for off-white cement. It also helps to have the iron oxide as ferrous oxide (FeO) which is obtained via slightly reducing conditions in the kiln, i.e., operating with zero excess oxygen at the kiln exit. This gives the clinker and cement a green tinge. Other metallic oxides such as Cr<sub>2</sub>O<sub>3</sub> (green), MnO (pink), TiO<sub>2</sub> (white), etc., in trace content, can also give colour tinges, so for a given project it is best to use cement from a single batch.