Coloured cement is manufactured by mixing pigments like chromium oxide, cobalt, iron oxide, or manganese dioxide at 5-10% by weight with ordinary Portland cement to produce different colours. The amount of pigment used depends on the desired shade. White cement is made from pure limestone and clay without iron oxides or other pigments, and the kiln is fired with oil instead of coal to avoid contamination, giving it a milky white appearance. White cement has similar strength and setting time to ordinary Portland cement and is used for highways, curbs, and ornamental and cast stone work.