Back Trap Mottle

A printing defect similar to mottle that occurs on multiple-unit offset presses, caused by non-uniform ink setting when the paper is still moving through the press and is aggravated by the use of quick-set inks and coated papers that promote the quick setting of ink. When the blanket on the last printing unit contacts the paper, it disturbs the print, but not uniformly, which produces the mottled appearance. BTM can be reduced by using an ink that does not set as quickly, or by using paper with a different coating formulation.

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