Glass Color Standards and a Uniform Chromaticity Scale for Sugar Products*

Abstract

Color specifications for the official glass color standards of the U. S. Department of Agriculture for extracted honey, maple sirup, sugarcane sirup, and sugarcane molasses are presented. These standards are used for rapid classification of samples according to chromaticity. The chromaticities of the standards are widely and irregularly spaced along the sugar products locus on the CIE chromaticity diagram. Continuous single-number scales for color used in the sugar industry are based either on absorption measurements at specified wavelengths or on small-difference colorimetry. The uniform color scale of “NBS units of sugar color,” proposed by Deitz and based on the Adams color-difference formula, is useful as presently formulated only for the lighter colors. In the present paper a greatly extended scale of uniform chromaticity, based on MacAdam’s data, is presented for application to solutions of sugar products. Loci of points on the CIE diagram differing from the achromatic point by 5, 10, 15, ⋯, 220 units of chromaticity difference are established, and their intersections with an average locus of sugar products are determined. Forty-five glass color standards having chromaticities close to these intersections and thus spaced 5 units apart on the scale are described. The number of MacAdam units of sugar chromaticity, ΔS, for a given sample can be estimated by three methods: by interpolation between the aforementioned loci on the CIE diagram, if the chromaticity coordinates of the sample are known; by visual comparison with the 45 glass standards of known ΔS; and by measuring absorbancy of the sample at 420, 560, or 720 mμ and referring to graphs relating absorbancy to ΔS, if turbidity is negligible.