Test Methods and Considerations for Mechanical Ghosting in Lithography

A mechanical ghosting test form has been developed. The form has been used in a large number of tests to evaluate many of the factors that influence mechanical ghosting on lithographic presses. Ink starvation ghosting is the occurrence of unwanted patterns of higher or lower density created by the job layout, combined with the press' inking ability. Mechanical ghosts can be seen in heavy solids or in heavy process work on both single and multicolor presses. The test form has proven successful in evaluating ink, ink film thickness, pigment, fountain solution, overall inking system, and the dampening system. A number of suggestions have been given to help reduce mechanical ghosting, including use of opaque inks wherever possible, reduction of ink strength, use of compressible blankets, and if possible, increasing roller size.