How to Prepare Files for Flawless Litho Printing

Why Litho Punishes Sloppy Files

Lithographic printing is a wonderfully industrial craft. Ink, water and aluminium plates come together on a press the size of a small van, and at the end you get sheets with a richness and consistency that digital printing struggles to match. It is also, per unit, the most economical way to print once you get past a few hundred copies.

What litho is not, however, is forgiving. Setting up a press involves making plates, mixing inks, adjusting register and running a make-ready sequence that can chew through hundreds of sheets before everyone is happy. If something is wrong with your artwork, it usually becomes obvious at that point — and the fix is not a quick tweak in the studio, it is a new set of plates and a reprint.

The reassuring news is that almost every litho disaster can be traced back to a handful of file preparation oversights. Spend ten minutes on the checks below and you will save yourself a great deal of grief, money and awkward phone calls.

Bleed and Crop Marks: Getting the Edges Right

Bleed is the extra margin of artwork that sits beyond the finished trim size, giving the guillotine something to cut into. The UK standard is 3mm of bleed on every edge where ink reaches the edge of the page. Some printers ask for 5mm on thicker stocks or jobs with unusual finishing, so always check the spec rather than assuming.

Set the document size to the finished size and add bleed in your document setup — never by scaling the artwork up. Keep crop marks offset from the trim (the default in most applications is 3mm) and include registration marks and colour bars only if your printer has asked for them.

• Check that background colours, images and rule-offs all extend past the trim line into the bleed. A background that stops exactly at the trim will show a sliver of white once the guillotine does its work.
• Keep text and important detail at least 5mm inside the trim. Trimming tolerance is typically plus or minus 1mm, and that is enough to slice through a headline you placed too close to the edge.
• Think carefully about borders and frames. A thin, even border around a page will look visibly uneven after trimming. Either make it chunky and bold, or let it intentionally bleed off the page.

Colour Mode: CMYK, Spot and the Black Trap

Commercial litho presses print with process inks — cyan, magenta, yellow and black — or with spot colours mixed to a reference, or a combination of both. Everything you send should be prepared accordingly.

Convert all colour to CMYK unless you are deliberately using a spot ink. Keep an eye on total ink coverage: on coated stock, aim for no more than around 300%, and on uncoated stock, 240–260%. Anything heavier may not dry properly and can set off onto the reverse of the sheet.

Black deserves special attention:

• Body text and small type should be 100% black only. Building a four-colour black into small text invites misregistration and fuzzy edges.
• Large solid black areas look richer with a "rich black" build, such as 40C 30M 30Y 100K. Ask your printer for their preferred recipe — it varies with press and stock.
• If you are using a spot colour, make sure the swatch in your file is a genuine spot swatch, not a CMYK colour simply named after a Pantone reference. That mistake finds its way into print far too often.

Resolution and Image Quality

Litho plates are made from high-resolution imaging, so low-resolution images have nowhere to hide. Aim for an effective resolution of 300ppi at final printed size. The word "effective" matters: a 300ppi image scaled to 200% becomes 150ppi on the page, and it will look soft.

Line art, bitmap logos and screenshots need more — around 1200ppi — because their hard edges show every pixel. Never upscale an image in the hope of rescuing it. Resampling adds no detail; it just makes a soft image bigger and softer.

Also decide early whether your printer wants a packaged folder with linked images and fonts, or a single PDF with everything embedded. Both work, but a missing link or a substituted font is the sort of thing that gets discovered at 4pm on the day before your deadline.

Fonts, Overprint and PDF Export

Embed your fonts, or convert them to outlines and keep a live-text version for your own records. Avoid faux bold and faux italic — genuine weights and styles only. Fine hairlines, delicate serifs and thin scripts can fill in on press, and reverse type (light text on a dark background) needs a little extra weight and size to hold its shape as ink spreads.

Check your overprint settings before you export. White objects often overprint by default in some applications, which makes them invisible against anything beneath. Turn on overprint preview and look at the job carefully.

For export, PDF/X-1a or PDF/X-4 are the safe choices for litho. Your printer will have a preference, particularly if your artwork uses transparency, drop shadows or soft edges. Confirm the trim and bleed boxes are set correctly in the PDF, and that no RGB sneakily survives the conversion.

A Final Ten-Minute Pre-Flight Check

Before you send anything, run through this list:

• Document size matches the finished size, with 3mm bleed added in setup.
• Crop marks present and correctly offset; no stray marks inside the trim.
• All colour in CMYK or a genuine spot swatch; total ink coverage within limits.
• Body text in 100% black; rich black used only on large areas.
• Images at 300ppi effective, line art at 1200ppi, nothing upscaled.
• Fonts embedded or outlined; no faux styles.
• Overprint preview checked.
• PDF exported to the printer's preferred standard with correct boxes.

It is also worth talking to your printer before you finish the design, not after. They will happily tell you their preferred PDF standard, their bleed requirement and their recommended black build. For colour-critical work, ask for a hard-copy proof rather than trusting your monitor — screens flatter everything. Do these things and your files will land on the press ready to go, which is exactly where you want them.