Color Reversions in Wool After Exposure to Light or Heat

Abstract

Unbleached wool appears to resist color changes by heat or light, in that the yellowing or bleaching caused thereby lessens during storage, the color tending to revert to the original. Reflectance measurements and visual comparison show that wool, after being yellowed by heat, by 315-m μ uv (or greened by 254-m μ uv, as shown previously) loses much of its pigment with time. In contrast, pigment eliminated during bleaching by 365 m μ uv, by 436 m μ visible blue-violet, or by total Berkeley sunlight is regained with varying rapidity during storage. These reversions in either direction can be so rapid and extensive that they cause large errors in measurement and can make results misleading. The reversions are simultaneous with, and opposite to, the primary color changes and, when too rapid, cannot be evaluated easily. Rever sion, a little-known phenomenon, may be general—not confined to wool, type of treament, or color. An awareness thereof may lessen errors by proper timing of measurements.