Coal is a fossilised product of decomposed plant and forest growth under marshy conditions. Coal is not a single material of one chemical composition but is a range of natural solids, which are rich in carbon. These carbons are part of a metamorphic series extending from Peat to Diamond with different total carbon content which can increase from about 50% to over 90%.

Coal Powder is used to reduce the production of Burn-on. The practice of adding pulverised coal to greensand in order to improve surface finish is as old as foundry industry itself. It is also used to eliminate expansion-type defects like metal penetration. When molten iron is poured into a greensand mould containing Coal, the input of heat causes the evolution of reducing gases into the mould cavity and these prevent the formation of iron oxide, which is thought to be an intermediate stage in the production of burn-on. As the oxygen supply in the mould is limited, sooting results and a thin layer of lustrous carbon is condensed onto the mould surface from the hydrocarbon gases. This layer acts as a refractory barrier between the metal and the sand thereby improving surface finish. In the final stage, Coal begins to coke near to the mould surface and in doing so it softens and expands. This happens at the same time as the critical quartz expansion takes place in the surrounding base silica sand and it allows re-adjustment of the sand grains and thus helps to control expansion-type defects.