An Investigation into the Cause and Cure of Random Toning in Newspaper Printing

A series of tests has been carried out in an endeavor to determine the root cause of random toning in offset newspaper printing. The work, which took place over a nine-month period, included printing and platemaking experiments in five different newspaper plants and two commercial printing plants. The plates used were primarily of the wipe-on diazo type. The basic concern has been found to be one of scumming, that is, of ink particles bonding to non-image plate areas. The fountain solution is no longer able to maintain the film of desensitizing agent on the non-image surface. Possible solutions to the problem include suggestions on gumming plates, and the use of plates with a better protective treatment. Printers can also post-expose plates, and rollup plates with ink when stopping the press.