The Printing Smoothness of Paper.

The printing smoothness of paper is a measure of how well it conforms to the plate surface and accepts a full ink image under printing conditions. Since the usual bench tests for smoothness give inadequate correlation with the press performance of papers, proof press tests have been devised to simulate the performance behavior. The proof press test prints are commonly evaluated by reflectance measurements which confuse smoothness with ink holdout. More meaningful analysis requires separation of these two properties. The ink holdout can be evaluated from a full coverage print, while the printing smoothness can be obtained from the amount of break. Prints were scanned with a modified Scan-a graver to produce strip chart traces of reflectance variations. Several functions of these data were studied for correlation with visual evaluation of break. Correlation of greater than 0.90 were obtained with out-of-limits reflectance. An integrating scanner was successful in measuring this quantity directly and in correlating with break obtained in halftones.