This International Standard specifies an instrumental method for determining the yellowness index and change in yellowness index on clear, translucent, or opaque plastics. NOTE 1 Specimen shapes can include moulded plaques or discs, films, sheets, powders, and pellets. Plaque, disc, film, and sheet specimens can have smooth, matt, or patterned surfaces. Fluorescent plastics are not permitted. NOTE 2 Change in yellowness index is often used to evaluate the effect of environment, e.g. heat, UV exposure, etc., on colour stability.