AVOIDING SET-OFF
‘Set-off’ is the marking of the underside of a sheet caused by the transfer of ink from the
sheet on which it lays. It can occur when pressure is applied during guillotining or simply
while the paper is stacked. Set-off is caused by the fact that the ink is still wet, and is most
prevalent on uncoated stocks like letterheads. Our process adds an extra gloss or silk coating
to all jobs printed on coated paper. This reduces the likelihood of set-off occurring, but you
should still be careful with which colours you choose, and in most cases you will be fine if
you limit your choices to the colours on our colour chart.
Let’s just remind ourselves of how process colour is created. As an example, a mid blue colour
consists of 100% cyan ink, 72% magenta ink and 10% black ink. If we add these percentages
together, we can work out that mid-blue has a total ink coverage of 182% (100% + 72%
+ 10%). The maximum ink coverage that is possible is 400% (which is of course 100%C,
100%M, 100%Y and 100%K).
++=
BLUE
100% Cyan 72% Magenta 10% Black
We have some guidelines to help avoid set-off. Our recommended ink coverage limit is
225%. This means that, wherever possible, the colours you use should contain less than a
total of 225% when you add together cyan, magenta, yellow and black. When it comes to
black ink, there are other considerations – see page 08.
On coated stocks you can use colours made up from more than 225%, but less than 300%
in smaller areas (such as headline text or logos), but you may run into problems if you were
to use large areas. Treat with caution, and if possible use lighter colours. Use the eyedropper
tool in Photoshop to check the darkest area of your image.
Please don’t use colours above 300% – you’re putting a lot of ink on to the page, and our
quick turnaround may mean that your job doesn’t have time to dry before it is cut. At ink
levels above 300%, your job may even begin to adversely affect other jobs printed at the same
time. If this is the case, we may be forced to quarantine your job at the print stage. Please
ask for advice if you are unsure.
You may be surprised to learn that you can perform ‘under colour removal’ to minimise the
amount of ink being put onto the page, but keeping the colour the same. You can find in-
depth discussions on these subject at www.adobe.com/support/
07
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