This may sound simple, but what makes white cement white?
The answer is somewhat complicated. Normal portland cement is manufactured as a combination of the elements calcium, silicon, aluminum, and iron. Of this combination the component tetracalcium aluminumferrate (4 CaO AlO
3) is chiefly responsible for the normal grey color of cement. If there were no trace at all of this component the cement would be pure white. To remove the component makes it virtually impossible to achieve a perfect cement. Therefore any iron still present is converted from the ferric to the ferrous state. One way of doing this is by reducing the length of the cooling process by spraying in oil so that any iron present is oxidized by its acidity. Milling must be done under exceptionally clean conditions. Despite the most careful processing, however, it is almost impossible for a manufacturer to avoid some slight color nuance. Usually a pigment such as titanium oxide is added to obtain a standard degree of whiteness.