Abstract
The color of pulp is important as a criterion of its quality. Usually in factories, the color of a pulp has been determined by visually comparing the sample with the “Standard white”(MgO Plate) or by measuring the reflectance at one wave length with Pulfrich Photometer.
But the former method cannot represent quantitatively the color difference of a pulp to another, and the latter cannot distinguish bright reddish pulp from dark grey one.
Generally the color of a matter can be completely represented by three quantities, in I.C.I. system, that is Luminosity, Purity and Dominant wave length.
But in calculating these quantities the spectral reflectance of a matter is necessary, which is obtained by a spectrophotometer, such as G.E. Recording Spectrophotometer.
This measurement is too troublesome to do in a factory.
§ The result obtained by G.E. Photometer shows that ordinary Rayon Pulps have nearly flat spectral reflectance curve with slight low reflectance at the short wave length region and that the color difference lies chiefly in “Luminosity” and “Dominant wave length”. Purity has almost same value throughout the range.
Therefore the reflectance at a definite wave length-such as 55omμ (RG) and the ratio of reflectances for blue and red lights (r=RB/RR ) are sufficient to represent the color characteristics of a Rayon Pulp, where RB and RR are respectively spectral reflectance at 450mμ and 630μ.
The large value of RG means that the pulp is bright and the small value of r means that the pulp is reddish.
§ To obtain RG and r, each of three monochromatized lights from 200W tungsten lamp with monochromatic filters is projected alternatively on the sample and on the “Standard white plate” and the reflected light being receieved by Sb-Cs photoelectric cells, the ratio of the amplified output currents is measured.
The results of experiments are shown in Tab. 1.
