Print & production
Marks, overprint & rich black
Three small production details decide whether a PDF sails through a printer's prepress or bounces back with questions: the marks that tell the finisher where to cut, the overprint behaviour that keeps technical inks from punching holes in your artwork, and the rich black recipe that makes large dark areas look genuinely black. All three live in the Print (CMYK) side of the Export dialog.
Why marks exist
Marks sit outside the trim, in the bleed and slug area, so they never appear on the finished piece. There are two kinds, and they do different jobs:
- Crop marks are the short corner ticks that show the finisher exactly where to guillotine the sheet down to trim size.
- Registration marks are the small crosshair-and-target symbols the press operator uses to confirm every ink plate — cyan, magenta, yellow, black and any spot — is landing in the same place. If the plates drift, the registration mark shows it instantly.
Because both must stay clear of the live artwork, they belong in the margin beyond your bleed edge.
Turning marks on
In the Export dialog, choose PDF with the Print (CMYK) color space, then flip on Crop & registration marks. It is off by default, and that default is deliberate: many modern printers impose your file onto their own sheets and add marks themselves — they often prefer a file without marks so yours don't collide with theirs.
Ask your print provider before you enable marks. If they impose and cut on their own equipment, send a clean file with just bleed. If they want you to supply marks, turn them on.
Mark offset
When marks are on, a Mark offset field appears just beneath the toggle. It pushes the marks away from the trim edge by the distance you set, in millimetres, so they never overlap bleed artwork.
The default is 3 mm, which suits the standard 3 mm bleed. If you run a larger bleed — common on die-cut labels and packaging — increase the offset to at least match it, so the crop ticks sit outside the bleed rather than on top of it. See Document setup & bleed for setting the bleed itself.
Knockout vs overprint
By default, when one color sits on top of another, the top ink knocks out the ink beneath it — the press leaves a hole in the lower plate exactly the shape of the top object, so the two inks never mix. That is the right behaviour for most artwork.
Overprint does the opposite: the top ink prints directly on top of the ink below, with nothing removed underneath. This matters enormously for technical and finishing inks — die lines, varnish, spot UV and white — which must mark or coat the piece without cutting a hole in the design they sit over.
| Behaviour | What the press does | Use it for |
|---|---|---|
| Knockout (default) | Removes the ink beneath the top object | Normal opaque artwork |
| Overprint | Prints the top ink over the ink beneath | Die lines, varnish, spot UV, white ink |
Swatches you create for these finishing inks default to overprint for exactly this reason. In the color panel the hint reads: "Technical inks (die lines, varnish, white) usually overprint so the artwork beneath prints intact." See Spot colors & print separations and Cut contours & dielines for how those inks are set up.
The Overprint / rich black control
The Print (CMYK) options include an Overprint / rich black checkbox, which is on by default. Keep it on: it honours the overprint flags on your technical and spot inks during export, and applies the correct treatment to rich blacks. There is rarely a reason to disable it unless a printer explicitly asks for a knockout-only file.
Rich black explained
A single 100% K black looks solid on small text, but across a large filled area it prints as a slightly washed, warm dark grey — one ink can only lay down so much density.
A rich black fixes this by adding cyan, magenta and yellow underneath the black, so the area reads as a deep, neutral black. A common recipe is roughly C40 M30 Y30 K100. The catch is total ink: those channels add up, and most presses cap total area coverage near 300%. Popcorn Editor's high-ink-coverage warning ("Most presses cap total ink near 300%") flags recipes that go too heavy — a rich black should stay under that ceiling. See RGB vs CMYK color modes for how the app soft-proofs and warns on ink coverage.
When to keep it simple
Reserve rich black for large solid black areas. For small text and hairline rules, use plain 100% K — a multi-ink black on fine detail risks a misregistration halo, where a sliver of cyan or magenta peeks out at the edge if the plates shift even slightly. One ink can't misregister against itself.
Marks on tiled sheets
If you use Step & repeat (imposition) to gang many copies onto one press sheet, marks are drawn only on the outer perimeter of the tiled block. Interior ticks are suppressed so they never overprint a neighbouring piece — you get clean trim marks around the block, not a grid of overlapping ones.
Where to go next
With marks and overprint settled, put it all together in Exporting a print-ready PDF, or make sure your finishing inks are separating correctly in Spot colors & print separations.