If you hear a printer use the term
trapping, they are probably not talking about trapping beavers.
The term
trapping to printers means printing ink over ink.
If you look at a printed piece that, let's say has a black solid panel
and inside that panel there is red text. You may or may not see a small
white line between the black and red. If you see this white line, it is
probably because the
printer did not trap the job properly.
In this scenario, it is necessary for the
printer to
increase the width of the stroke of the red text so that it actually
overlaps the black background slightly. Because the black background is
a darker color, your eye does not see the red text as being bolder. The
amount of overlap is very slight, approx .006" and is absolutely
necessary for colors that appear to touch each other. There are several
reasons why it is necessary.
As precise as
printing presses are, they are not perfect but an even larger reason is the movement of the sheet of
paper as it travels through the press. When
paper
travels through a press a tremendous amount of pressure is applied to
the sheet. In addition to pressure, moisture is also introduced to the
sheet.
Paper will stretch with pressure and actually swell with moisture. The .006" of trap is needed to cover for these variables.
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Written by Jay Atkinson
jay@odeecompany.com
The Odee Company
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