This part of EN 12625 specifies the test methods that shall be used for the instrumental determination of optical properties of tissue paper and tissue products.It also gives recommendations regarding relevant optical properties to be measured for different grades of tissue paper and tissue products and gives specific instructions for the preparation of test pieces (single-ply, multi-ply products) and for the optical measurements of creped products and embossed products, where special precautions may be necessary if the test pieces surfaces are uneven and if the materials are bulky so that air is entrapped between the sheets.