Improvement of Luster of Cotton

Abstract

Luster is not an "absolute" property of the cotton or the yarn, but depends on the sheerness of the fabric, as well as on the weave pattern. One of the reasons for the greater apparent luster of sheer fabrics or thin layers of yarn is that there is less opportunity for light to be scattered within thin layers than in its return from the lower parts of thick layers of yarn. Such scattering adds an approximately equal amount to the reflectances at all angles and so lowers the apparent contrast ratio for the thicker layers. At the opposite extreme, the reflectance of individual yarns can be determined, and it is demonstrated that yarn removed from the fabric has nearly the same luster as the original yarn, if the weaving crimp is removed. Weaving crimp by itself reduces the measured luster, tending in the same direction as the effect of cross-yarns. The measurement of contrast ratio in yarns correlates with the average of numerous judg ments by observers. For fabrics, the ability of the eye to see sparkle or high lights, and to find the angle of maximum reflection, gives visual judgment some features not possessed by the more simple types of physical measurement, although even with fabrics there is a large degree of correlation.