Light was found to bleach wool that had yellowed from a wide variety of causes. The spectrum of the bleaching light and, to a lesser extent, the chemistry of the pigment determine the rate. For rapid bleaching, light should contain no uv below 360 mμ, and preferably no uv at all, as this causes competitive yellowing. Photobleaching of wool previously exposed to uv at 254 mμ was found to be some 20,000 times faster than spontaneous dark bleaching (or reversion).
Coblentz, W.W. , Dorcas, M.J., and Hughes. C.W., Radiometric Measurements on the Carbon Arc and Other Light Sources Used in Phototherapy, Sci. Papers Bureau of Standards No. 539 (Nov. 19, 1926), vol. 21, pp. 535-562.
2.
Hirt, R.C., Schmitt, R.G., Searle, N.D., and Sullivan, A.P., Ultraviolet Spectral Energy Distributions of Natural Sunlight and Accelerated Test Light Sources, J. Opt. Soc. Am.50, 706-713 (1960).
3.
Launer, Herbert F., Photobleaching—A Common Basic Phenomenon , Nature218, 160-161 (1968).
4.
Launer, Herbert F., Spectral Conformity-A New Widespread Effect of Light, Nature218, 161-163 (1968).
5.
Launer, Herbert F., Effect of Light Upon Wool. Part IV: Bleaching and Yellowing by Sunlight, Textile Res. J.35, 395-400 (1965).
6.
Launer, Herbert F., Effect of Light Upon Wool. Part V: Yellowing and Bleaching by Ultraviolet and Visible Arc Light, Textile Res. J.35, 813-819 (1965).
7.
Launer, Herbert F., Effect of Light Upon Wool. Part VI: Spectral Conformity in Photobleaching of Wool, Textile Res. J.36, 606-611 (1966).
8.
Launer, Herbert F., Effects of Radiant Energy on Wool Color, Technical Wool Conference, Agricultural Research Service, ARS-74-29, U. S. Dept. Agr.; Nov. 1964, p. 71.
9.
Launer, Herbert F. and Wilson, William K., Photochemistry of Cellulose. Effects of Water and Oxygen in the Far and Near Ultraviolet Regions. J. Amer. Chem. Soc.71, 958-962 (1949) ; Photochemical Stability of Papers, J. Res. Nat'l. Bur. Std.30, 55-74 (1943).
10.
Lennox, F.G. , Inglis, A.S., and Holt, L.A., Studies in Wool Yellowing. Part XIII: Partial Bleaching with Visible Light. Textile Res. J.36, 837-843 (1966).
11.
Lennox, F.G. and King, M.G., Studies in Wool Yellowing. Part XXIII: UV Yellowing and Blue-Light Bleaching of Different Wools, Textile Res. J.38, 754-761 (1968).
12.
Stewart, R.G. , Light-Fugitive Yellow in Wool, Third Intern. Wool Textile Res. Conf., Paris , 1965, Section 2, pp. 143-153.
13.
Unpublished results by Glen F. Bailey and the writer, using a Cary 14 as a spectroradiometer.
