This International Standard specifies a method for the determination of the effective residual ink concentration (ERIC number) by infrared reflectance measurement. This International Standard is applicable to all types of deinked, recycled pulp and to sheets of machine-made paper made from recycled pulp, where the residual ink is black. The method is applicable to materials available in sheet form only if the opacity at 950 nm is less than 97 %. The ERIC number obtained is dependent on the distribution of ink particle sizes, and the method is most effective for submicron particles. The value obtained is reliable only if the test material is uniform in ink distribution, formation, and grammage such that presenting different parts of the sheet to the measuring aperture of the reflectometer produces very similar readings.