Details:
Summary:
Color measurements of laboratory prepared proof samples were made for sheetfed paste and type C gravure liquid inks under carefully controlled conditions. Using the same ink, the same paper, and the same procedures, significant differences were found in CIE L*,a*,b* and Delta E* colorimetric values. Significant differences were also observed in sequential proof samples made at the same time by the same operator. Color differences between laboratories were minimized when nine replicate samples were averaged. Color measurements of proof samples made with two commercial papers recommended by SWOP and produced to the same specifications (Paper A and Paper B) showed Paper B to have a smoother surface than Paper A. These results attest to the critical importance of using paper from the same roll, when comparing color data between laboratories. In order to evaluate the effect of using different instruments on color variation, all proofs were also measured with one instrument and one operator. These results show a slight but significant reduction in color variation, indicating that the error introduced by using different instruments is not large. Since the same samples of ink were used in each of the laboratories, these results demonstrate that there are considerable differences in color not due to the ink, but to variations in the substrate and the method used to apply the ink. Color variation between laboratories can be minimized by using mechanical ink applicators, the same paper substrate, and most importantly, averaging the results of several replicate samples.