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What are printer's marks? Trim, registration and colour bar marks

Look at the edges of a printed sheet and, besides the job itself, you will see short lines, crosshairs and little colour squares. These are printer's marks. They never appear on the finished product and are trimmed away; but the press operator, the cutter and the binder all rely on them to do their work right.

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Trim marks

Trim marks are short lines showing where the net size of the job ends. They sit at the corners, on the extension of the job's edges, without entering the job.

A few millimetres are left between the marks and the job. If a mark reaches into the bleed, a small line can remain on the edge after cutting. When many jobs are laid out on one sheet, the marks can sit at the outer corners of the block instead of at every job's corner; the cuts in between are measured from those outer marks.

Registration marks

In colour printing each colour is printed from its own plate. Registration marks, usually a crosshair inside a circle, show whether the colours sit exactly on top of each other. When they are off, coloured fringes appear around the mark.

These marks have to print on every plate. That is why they use the registration colour: a special colour that prints at 100% on all plates. Drawing the marks in black alone makes it impossible to check how the other colours line up.

Colour bars

A colour bar is a strip of small colour patches printed across the edge of the sheet. The press operator measures density on these patches and adjusts the ink zone by zone.

The bar usually goes on the strip outside the job on the gripper or tail side. When choosing the sheet size, leave room for that strip too.

Fold and crease marks

On jobs that will be folded, such as brochures or signatures, fold positions are marked with dashed lines at the edge of the sheet. The binder sets up the folding machine from these marks.

On boxes and packaging, cut and crease are separate lines; they are carried not as printer's marks but as separate spot colours on the die line layer, so they never mix with the print.

Placing the marks

A few rules make sure the marks do their job:

  • Place marks outside the bleed, never inside the job.
  • Registration marks should be in the registration colour, not black or a four-colour mix.
  • Keep marks and artwork out of the gripper margin; the press holds the sheet there.
  • With many jobs on a sheet, gather the marks at the outer corners of the block instead of crowding the gaps between jobs.

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