The Rates of Fading of the S.D.C. Light Fastness Standards (B. S. 1006)

The rates of fading of the S.D.C. light, fastness standards 1 to 6 have been determined by exposing portion of'each standard for different times in a fading lamp and finding the difference between the exposed and unexposed patterns, optically and visually. The reflectance rurves of the patterns have been obtained, and two colour difference formulæ used to calculate the colour change, on exposure, in just perceptible steps. It is shown that the results obtained optically do not correspond to the obtained difference. In view of this, the differences I have been estimated visually against a grey scale, and the results obtained show that the spacing of the standards 1 to 6 is satisfactory.