trim marks
Trim marks are the short lines printed outside the finished page to show where the blade goes.
In more detail
Four corners, eight short lines: each pair points at one corner of the finished page without touching it. Whoever stands at the guillotine lines the blade up on them, and the marks go into the waste with the rest of the margin.
They have to stand outside the colour that runs past the cut, which is why a press sheet is bigger than the finished page by more than the bleed alone: so much for the ink to run past the blade, and the rest so the marks have room beyond it.
What it does on a real document
A file made for a press draws them on the sheet itself, in the margin the trade calls waste, at the four corners of the page it declares as finished. A sheet of labels the paper maker has already cut carries them too, in the margins, so that what is printed lands inside the pieces the die has made.
They are laid in every ink at once so that every plate carries them. A mark that came out on one plate only would line nothing up, and lining the plates up is the second thing they are for.
Where it comes from, and why
They are as old as cutting paper in stacks. What has changed is who draws them: the file does it now, in the same places, for the same pair of hands at the guillotine.
See it on a finished document
A sheet as it goes to the press A sheet of shelf labels The rules behind this word, and the texts they are read from
Glossary
- CMYK
- The four inks a printing press lays down: cyan, magenta, yellow and black. A screen mixes light instead, so a document going to a press states its colours in inks, not in screen colours.
- printing plate
- A press prints one ink at a time, from a metal sheet carrying the marks that ink is to leave: that sheet is the plate. A four-colour job is four plates, laid one over the other on the same paper. A file for a press says which ink each mark belongs to, because that is what decides which plate carries it.
- bleed
- The colour that runs past the line the blade will cut, so that a cut a hair out of place still lands in ink rather than beside it. Three millimetres is the usual amount. Without it, a page printed to its edge comes back with a white sliver down one side.