Details:
Summary:
Color measurements of laboratory prepared proof samples made for heatset web offset inks and water base flexo inks under carefully controlled conditions. Using the same ink, the same paper, and the same procedures differences were found in L*, a*, b* valued and delta E* colorimetric values. Differences were also observed in sequential proof samples made at the same laboratory by the same operator. Significant color differences were also observed in sequential proof samples made at the same laboratory by the same operator. Color differences between laboratories were minimized when nine replicate proof samples were averaged. Significant color differences were also observed in sequential proof samples made at the same laboratory by the same operator. Color differences between laboratories were minimized when nine replicate proof samples were averaged. Color measurement of proof samples made with the heatset inks with two commercial papers recommended by SWOP and produced to the same specifications (Paper A and Paper B) also showed differences. Variation within a given paper was less for Paper B than Paper A. Photomicrographs showed paper B to have a smoother surface than Paper A. These results attest to the critical importance of using the same paper from the same manufacturer, and preferably from the same roll when comparing color data between laboratories. Since the same samples of ink were used in each of the laboratories, these results demonstrate that there are differences in color not due to the ink, but to variations in the substrate and the method used to apply the ink. Color variations can be minimized by using mechanical ink applicators, the same paper substrate, and most importantly averaging the results of several replicate samples.