This International Standard specifies a method for the determination of the light transmittance of the toluene extract from carbon black for use in the rubber industry, as a means of measuring the discolouration caused by the extractable matter. The light transmittance value provides an estimate of the degree of discolouration caused by the toluene-extractable matter present on the surface of the carbon black. This method may not be applicable to carbon blacks with a high extractable-matter content.