alignment crosses

In more detail

Each ink goes down in a pass of its own, and the sheet has to come back to the very same place each time. A cross printed by every plate at the same spot is how that is checked: if the crosses fall exactly on one another, the inks agree; if one of them sits a hair to the side, everything printed in that ink does too.

They stand outside the cut, on the part of the sheet the blade takes away, so nothing of them shows on the finished page. They answer a different question from the trim marks beside them: those say where the blade goes, these say whether the inks are on top of one another.

What it does on a real document

A file cannot draw them in black, and this is the part that surprises people. Black is one plate out of four: a cross laid in black comes out on the black plate and on no other, and lines up with nothing. What is wanted is a mark that every plate carries.

There are two ways to ask for that. A name is set aside for an ink meaning all of them at once, and a mark said in it is laid on every plate whatever inks the job runs on — which is what the two-ink sample of the gallery uses for its four crosses. The other way is to ask for every usual ink at full strength, which comes to the same thing on a job printed in those four.

Where it comes from, and why

They are as old as printing a sheet in more than one colour, and the trade's word for what they check is register. A sheet out of register is easy to recognise without knowing any of this: the letters carry a coloured fringe on one side, and a photograph looks faintly doubled, as though it had been printed twice a hair apart.

The operator watches them through the run and brings the press back when it drifts, which is why they are printed on the waste rather than left off: a check nobody can see is a check nobody makes.

See it on a finished document

Inks on plates of their own The rules behind this word, and the texts they are read from