ISO 3908:2009 specifies a gravimetric method for the determination of the mass fraction of insoluble (free) carbon in carbides and hardmetals. This method is applicable to carbides of hafnium, molybdenum, niobium, tantalum, titanium, vanadium, tungsten and zirconium, mixtures of these carbides and binder metals, free of lubricant, and all grades of presintered or sintered hardmetals, produced from these carbides, having a mass fraction of insoluble carbon between 0,02 % and 0,5 %.