The flotation process is a method of separating mineral ores from unwanted rock and other material. The ore as mined is finely ground and then mixed with water, to which chemicals called wetting agents are added. The mixture is aerated to make a froth. The required ore particles stick to the bubbles and float, and are skimmed off the surface; waste rock sinks to the bottom. The method works because of differences in wetting properties (see surface tension between the various components.