Standard fabrics for light fastness, blue wool cloth NO.1-NO.8 series products are dyed wool fabrics with special blue dyes, providing blue wool with a range from very low light fastness to extremely high light fastness. They form an ordinal series from 1 to 8, with 1 representing the lowest light fastness to 8 representing the highest light fastness. This product can be used to measure the color change of the gray scale to classify the fabric, which is related to the performance during use. Used in ISO 105 B series tests