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Accurately assessing the color quality of printed products becomes intricate when optical brightening agents (OBAs) are introduced in papers, as diverse interactions occur among different ink pigments and papers containing OBAs due to variations in ink formulation chemistries. Specifically, alkali‐based pigments, commonly used as spot colors, are carefully formulated to ensure consistency across production batches. The presence of OBAs, which absorb ultraviolet light and emit it in the visible spectrum, significantly affects color perception and accuracy on paper when interacting with these inks. This research marks an initial investigation into how OBAs in paper influence the color accuracy of five distinct alkali‐based spot color paste inks using a Little Joe ink proofer. The research examines the physical, optical, and colorimetric characteristics of two paper samples‐one with OBA and one without‐ and analyzes the colorimetric changes occurring during the ink drying process. The results indicate that reflex blue, purple, and violet spot colors achieved acceptable delta E (ΔE00) value of below 3 on non‐OBA paper, with rubine red being on the borderline at 3.1 after 48 h. In contrast, purple, rhodamine red and violet achieved acceptable ΔE00 below 3 on high OBA paper. The distinct behavior exhibited by certain inks led to the conclusion that achieving a consistent proofing procedure across diverse alkali‐based ink formulations is impractical. [ABSTRACT FROM AUTHOR]

Automated color measurement systems have become significant components of offset lithographic printing presses for better process control and reduced job waste. Some European press manufacturers are known to offer automated color measurement equipment that is confined to polarized density readings, which is uncommon in US. Introducing polarized densitometry into an environment where unpolarized densitometry is utilized can be problematic. Print professionals are on the lookout for a solution that is evidenced by a recent feature in a post from the IDEAlliance G7 Professionals forum seeking for a methodology to convert polarized to unpolarized readings. The present study applies the Bland–Altman method together with other statistical analyses to determine if a conversion between polarized and unpolarized densitometry can be established within a limited set of parameters. Three spectrodensitometers were used to record densitometric readings of wet and dry process inks on coated and uncoated drawdown proofs. The results showed that coated papers had significantly less variation between instruments compared to uncoated papers. Wet inks had more minor variations compared to dry inks. Furthermore, pure difference values and a Mann–Whitney U test indicated differences between unpolarized and polarized densitometric readings in all cases. Finally, t‐tests performed on the resulting difference data for both unpolarized versus polarized and unpolarized versus predicted polarized that showed fixed bias by means of the computed p‐values. [ABSTRACT FROM AUTHOR]