Abstract
It was found that the formulae given by Norton-Nichols is the best among several formulae which express numerically the degrees of silk yellowing which correlates well with sensuous assessment.
There was a difference in wavelength dependence between yellowing and degradation, i.e., yellowing of silk occurred in the region of wavelength from 230mμ to 350mμ (max. 309_??_322mμ) and degradation of silk occurred in the region from 220mμ to 370mμ(max. 244_??_257mμ).
It appears that silk is, to some degree, bleached by visible light.
And yellowness index increased with increasing loss of tryptophan in silk fibroin, and yellowing by irradiation of Xenon lamp was greater than by that of carbon arc when compared under the same amount of the loss.
Finally, it was found that oxygen plays an important role in silk yellowing by irradiation of Xenon lamp.
