Brick manufacturers also offer a wide variety of colours from which to choose. Colour is determined by raw materials and firing temperatures. Colours range from reds and burgundies to whites and buffs, with many manufacturers producing more than 100 colours. Many of these colour variations are created during the firing process when temperature variations and the order in which the units are stacked in the kiln determine shades of light and dark. Sand, slurry or ceramic glazes can be applied to the surface to achieve colours not possible with some types of clay.