Effect of Light Upon Wool

In Berkeley, California, it was found that sunlight bleached wool during exposures of 1 to 150 sun-hr. However, when the visible light was excluded, wool was yellowed by the solar ultraviolet. Bleaching was increased by progressive exclusion of solar UV with various cut-off filters and was greatest with only visible light, the visible violet being the most effective. Solar UV below 311 mμ was the most yellowing. Thus, the net effect of sunlight upon wool varies with its spectral composition, and its variability in place and time probably explains the variable results, yellowing or bleaching, reported by others around the world. Full sunlight also bleached wet wool that, after a long induction period, turned yellow, apparently, in a dark-follow reaction.