A machine for cleaning coal and other materials that uses a dense fluid in which the coal floats and shale sinks. The fluid consists of water intimately mixed with sand (or finely ground magnetite or even shale) and agitated to maintain its consistency. The fluid has an effective specific gravity of 1.3 to 1.9. In general, coal from about 8 in (20.3 cm) down to 1 in (2.54 cm) is washed by dense medium, below 1 in by Baum washer, and below 0.75 mm (where cleaning is necessary) by froth flotation. Magnetite as the dense medium solid is preferred as it can be easily recovered by magnetic separators and also the upper limit of the specific gravity is higher (up to 2.0).