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Summary:
This paper summarizes the findings of a study of sheetfed lithographic printing attributes conducted by the Graphic Arts Technical Foundation (GATF). The study was undertaken to obtain a print profile for high quality sheetfed lithography. This profile is needed to establish attainable print specifications for this industry segment. Thirty-five GATF member companies printed a test form using different press/ink/paper combinations, and submitted 107different samples. Ink dryback, density aim points, dot gain, ink trapping, print contrast, gray balance, and color variation were all studied. Ink dryback was found to vary with different printing systems, but overall a small density loss can be expected as the sheets dry, especially in black. The industry was found to be running at density aim points lower than those set in the General Requirements for Applications in Offset Lithography (GRACoL) guidelines for all ink colors. The relationship of dot gain and screen ruling for black ink showed an increase in dot gain with finer screen rulings. Average midtone dot gains for 150-lpi printing were 20% for cyan, 20% for magenta, 20% for yellow; and 22% for black. Ink trapping on coated paper averaged 72 for blue, 89 for green, and 76 for red. The print contrast values were higher for coarser screen rulings. They were examined in relation to the solid ink densities, 50% dot gains, and 50%/75% dot gain ratios. Gray balance was found to be lower in cyan content than the gray values listed in the Specifications for Web Offset Publications (SWOP). The selected tertiary colors showed clear perceptual differences with different printing conditions. Differences of about 12 (E units from the target CIELAB coordinates can be expected when a screen build is sent to a random commercial offset lithographer.