Tips & Tricks: Mottling
When speaking of "mottling" or "back trap mottling", printers are
referring to a cloudy print output. The problem originates in paper
that is partially uneven and the resulting uneven absorption and
back split characteristics.
If the paper is spotted, or if a certain amount of cloudiness
is already present in the coating, then the printing ink will be
only partly absorbed. In four color sheetfed offset printing, the
printing result will back trap on the printing blankets of the
subsequent printing units. When an uneven penetration of printing
ink is especially pronounced, this will become visible after the
back trap process occurs, as an uneven print reproduction.
The problem of a "cloudy printout" is most prevalent in
offset printing. In order to isolate the printing paper as the
culprit, one must first determine if the visual appearance of the
cloudy printout matches up with the paper structure. This can be
done using backlighting, or under UV light. The absorption
characteristics of the printing ink on the paper in question can
also be made visible by resorting to a simple wipe test using
special wipe-test ink. In this way, proof that paper is the root
cause may be confirmed.
In cases where the cloudy printout is purely the result
of the paper being used, the solution is to change to an
alternative type of paper or contact your supplier.
Tips & Tricks
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