This part of ISO 12625 specifies testing procedures for the instrumental determination of brightness and colour of tissue paper and tissue products viewed in indoor daylight conditions. It also gives specific instructions for the preparation of test pieces (single-ply, multi-ply products) and for the optical measurements of products, where special precautions may be necessary. NOTE The properties called D65 brightness and colour are measured with an instrument adjusted to a much higher UV content than that specified in this part of ISO 12625. The measurements of D65 brightness and colour are described in ISO 12625-7.