A new technique for the measurement of show-through mottle of fine paper

Mottling within print-through and show-through is caused by the variability of the local optical properties of the sheet. This mottling is visually disturbing and a mark of poor paper quality. The ability to predict print-through mottle of printed paper by measuring show-through mottle on the unprinted sheet would be a valuable asset for paper machine control. We examined the relationship between print-through mottle and show-through mottle. We worked with nine samples of 60 lb. uncoated fine paper (90 g/m2), from various North American paper companies, that were printed on an offset press, 400K (400% Black), on both sides. A show-through mottle instrumental determination technique was developed using an existing Fast Fourier Transform-based algorithm. The nine samples examined were ranked similarly by the visual evaluation of print-through mottle and by the instrumental determination of show-through mottle. We thus established that show-through on the unprinted sheet can be used as a reliable predictor of print-through, therefore saving time and money for papermakers. We also found a significant two-sidedness in show-through for some of the samples.