Details:
Summary:
Unevenness within a single offset printed press sheet is the topic of this report. For offset printing, evenness across the cylinder is adjustable using the ink fountain keys. Affecting evenness aroun the cylinder is more difficult and in practice often ignored.
The question is whether the tolerances specified by standards can truly be met when solid densities and dot gain are not only measured on the single location of a color control bar, but when looking at the whole press sheet. A special test pattern was designed that samples the area of the whole press sheet at every ink key. The following parameters were evaluated for each of the CMYK colors: solid density, dot gain, doubling and the uniformity of the paper and measurement instrument itself.
Preliminary tests showed unevenness of up to +- .15 density units (with high inking), however, a much better controlled experiment showed deviations around the cylinder of about 0.08 density units.