An instrumental method for measurement of the changes in reflectance, chiefly in terms of the luminous reflectance (the CIE tristimulus value Y), is proposed as an objective method for measuring the rate of fading of the British Standard BS1006:1971 (ISO R105) blue-wool standards 1 through 6. A tentative relation of the change in Y value (delta Y) that corresponds to steps 1, 2 and 3 on the standard geometric grey scale (BS2662) is also noted. Measurement of the change in reflectance at the wavelengths of maximum absorption of the individual cloths or at 620 nm also yields satisfactory results. The curves of delta Y or deltaR₆₂₀ against time are linear over the total range of fading normally used in rating the degree of fading visually, that is, from a grey scale (BS2662:1961) change of less than 4 to slightly greater fading than grey scale 1. See also AATA 16-128.