This paper describes the results of an interlaboratory comparison of working standards made on behalf of Committee E-1.3.1. (Colorimetry) of the Commission Internationale de l’Eclairage. Thirty laboratories from 15 different countries participated and spectral reflectance (βλ), luminous reflectance (β), and chromaticity coordinates (x,y) were reported for four glossy ceramic tiles—near-white, light grey, dark grey, and near-black. The results have been analyzed in two groups depending on whether the illumination and light collection were directional or diffuse. A very considerable spread was found in each group of results, as well as a significant difference between the mean values of β in each group; the causes have been discussed. With a selected group of laboratories, however, the spread was very much smaller; use of calibrated white, grey, and near-black standards is recommended as a means of extending this agreement to laboratories which are not in a position to adopt all the refinements available to standardizing laboratories.
A. R. ROBERTSON and W. D. WRIGHT, "International Comparison of Working Standards for Colorimetry," J. Opt. Soc. Am. 55, 694-705 (1965)