The two methods are applicable to raw, compounded and vulcanized rubbers of the families described in ISO 1629. The principle of method A consists in heating a weighed test portion in a crucible over a gas burner, followed by volatilization of the decomposition products and transfer of the crucible to a muffle furnace. The crucible is heated until all the carbonaceous matter has been burnt off and constant mass is attained. In method B a weighed test portion is heated in a crucible in the presence of sulfuric acid, first by means of a gas burner and then in a muffle furnace as in method A. Platinum crucibles shall be used for ashing fluorine-containing and lithium-polymerized rubbers. Cancels and replaces the second edition ISO 247:1978, which contains three methods of determination.