Some aspects of the colour measurement of New Zealand wools, with emphasis on measurement by liquid scintillation spectrometry

Abstract

Abstract Greasy wool samples were collected from each of the main New Zealand breed types, viz. Merino, Corriedale, Perendale, fine crossbred, and strong crossbred, and after laboratory washing were visually graded as white, light yellow, medium yellow, or heavy yellow. The samples were measured in a reflectance colorimeter (tristimulus values X, Y ,Z recorded) and in a liquid scintillation spectrometer (LSS), which recorded blue reflectance (BR) and mean fibre diameter (FD). Differences in colour variates between breeds and between colour grades were examined by analysis of variance. Interrelationships between tristimulus values and relationships between tristimulus and LSS measurements were examined by correlation or regression as appropriate. There was no significant interaction between breed and colour grade for any variate. The heavy yellow grade was on average 8 units lower than the white grade for X and Y (brightness) and 20 units lower for Z and BR. Y-Z (yellowness) increased from 2 units for the white to 17 units for the heavy yellow grade. There was a precise positive regression of X on Y, indicating that the reporting of both values is superfluous. Y-Z and Y were strongly negatively correlated (r = -0.79 across breeds). There was a wide range in Y-Z relative to the range in Y, probably because the samples were selected solely on their degree of yellowness. There was a strong positive relationship between Y and Z. As FD increased, Y decreased significantly across breeds, but there was no consistent relationship between Y-Z and FD. There was a very close positive relationship between Z and BR (R2(adj) = 0.96). Although there was a close positive relationship between Y and BR and a close negative relationship between Y -Z and BR, in each instance the addition of FD improved the relationship. The multiple regressions accounted for 86 and 92070 of the variation in Y and Y-Z, respectively. Measurement with LSS predicts brightness and yellowness with an accuracy acceptable for most purposes in wool production research.