Preflight Checklist for Print-Ready Files: Colour Mode, Font Embedding & Overprint

Overview #

When a brand partner sends us artwork files, the first 30 minutes our prepress team spends on that file determines whether the job runs cleanly or generates costly corrections, reprints and schedule delays. Colour mode mismatches, unembedded fonts and incorrect overprint settings are the three most common file errors we catch — and all three are invisible to the brand’s design team until ink hits substrate. This guide covers exactly what we check, in what order, and what thresholds trigger a file rejection versus a correctable warning. It applies across our folding carton, rigid box label and flexible packaging print lines, and is most relevant to brand partners supplying PDF, AI or INDD source files for offset, digital or gravure production.

For a related specification, compare Prepress Preflight for Packaging: Resolution, Colour Space & Overprint Check Guide before finalising the packaging brief.

Colour Mode Verification: CMYK, Spot Channels and Total Ink Coverage #

The first check our prepress operator runs is colour mode. Every file destined for offset or gravure production must arrive in CMYK — not RGB, not Lab, not indexed colour. RGB-to-CMYK conversion done at our end without brand approval introduces unpredictable hue shifts, particularly in brand colours with high saturation in the red-orange and blue-violet ranges. We have seen RGB-submitted files where a brand’s hero red (R:220 G:35 B:35) converts to a CMYK build that reads 15% warmer under D50 viewing conditions than the brand’s approved Pantone reference.

For spot colours, we require all Pantone references to be specified using the current Pantone Matching System (PMS) library — specifically the Pantone+ Solid Coated or Solid Uncoated deck, depending on substrate. Pantone Legacy references (pre-2023 renaming) must be flagged and confirmed before plate output.

Total ink coverage (TIC) is a hard pass/fail threshold. Our standard limits by substrate:

Files exceeding these thresholds by more than 5% are returned for correction. Files within 5% of the limit are flagged as warnings and we discuss with the brand partner before proceeding.

We work to ISO 12647-2 (offset lithography) and ISO 12647-6 (flexographic printing) colour characterisation standards. Our G7 Master certification on our sheet-fed offset lines means our press operators target a maximum ΔE of 2.0 against the approved digital proof under D50/2° observer conditions.

Font Embedding, Outline Conversion and Minimum Type Size #

Unembedded fonts are the single most common file error we receive — roughly 40% of first-submission files from new brand partners have at least one missing or partially embedded font. When a font is not embedded and we do not hold that licence, our RIP substitutes a system font, which changes character spacing, line breaks and in some cases reverses out text that was designed to hold at small sizes.

Our preflight rule: all fonts must be embedded or converted to outlines before file submission. We use Enfocus PitStop Pro for automated preflight, and our font check flags any font with an embedding restriction flag set to “no embedding allowed” — these must be outlined by the brand’s designer before we can proceed.

Minimum type size thresholds we enforce:

• Positive text (dark ink on light ground): 5pt minimum for single-colour; 6pt minimum for multi-colour builds
• Reversed-out text (light on dark): 7pt minimum — below this, ink spread in offset printing closes counters in letters like ‘e’, ‘a’ and ‘B’
• Fine serif fonts reversed out: 8pt minimum — serif stroke width below 0.2mm fills in at standard offset ink viscosity (18–22 Pa·s at 25°C)
• Barcode human-readable text: minimum 8pt, font must be OCR-B or equivalent monospaced

For barcodes specifically, we verify against GS1 General Specifications — minimum X-dimension of 0.264mm for EAN-13 on retail packaging, with a bar width reduction (BWR) of 0.050–0.100mm applied at plate output depending on substrate absorbency. We run a barcode grade verification scan on press proofs targeting a minimum ISO/IEC 15416 grade of 1.5 (C) for retail, 2.5 (B) for premium brand packaging.

Overprint Settings, Trapping and Knockout Verification #

Overprint errors are the most technically damaging file fault we encounter — they are invisible on screen in normal preview mode and only appear at output. The two failure modes are opposite in effect:

Overprint ON when it should be OFF: A black headline set to overprint on a coloured background will print correctly. But a yellow panel set to overprint on a white background disappears entirely — the yellow inks over nothing and the white paper shows through. We have caught this on files where a designer accidentally enabled overprint on a large background panel.

Overprint OFF when it should be ON: 100% black text knocking out of a four-colour background creates misregister halos — a white fringe around every character when plates are even 0.15mm out of register. Our standard is to set all 100% K text below 24pt to overprint automatically at RIP, regardless of the file setting, using our PitStop fixup rules.

Our trapping parameters for sheet-fed offset:

These values are calibrated for our Heidelberg Speedmaster XL 106 sheet-fed offset press, which holds a register tolerance of ±0.10mm under normal production conditions. For flexographic and gravure lines, trap widths increase to 0.20–0.30mm due to wider register tolerance on web presses.

We reference FOGRA 51 (ISO 12647-2:2013 coated) as our standard characterisation dataset for proofing and press matching on coated substrates.

Specification Notes for Brand Partners #

When you brief us on a new print job, send us your artwork files alongside a completed file specification sheet that confirms: colour mode (CMYK or CMYK + spot), Pantone references with coated/uncoated designation, intended substrate, and any special finishing areas (foil, emboss, varnish) as separate layers or spot channels. The most common mistake we see is brands supplying RGB files exported from Canva or web-optimised workflows — these always require colour conversion, and we will not convert without your sign-off on a colour-matched proof.

Our standard preflight and proofing process: automated PitStop preflight report within 4 working hours of file receipt; digital soft proof (PDF with colour profile embedded) returned within 1–2 working days; physical Epson contract proof (ISO 12647-7 compliant) available within 3–5 working days for colour-critical jobs. Production lead time begins after your written proof approval — typically 15–20 working days for folding carton runs and 20–28 working days for rigid box or flexible packaging.

If your file has correctable issues, we send a marked-up preflight report and hold the job until you resubmit. We do not proceed to plate output on a file with hard-fail errors.

Frequently Asked Questions #

Q1: What total ink coverage limit should I design to for a coated folding carton?
A: Design to a maximum of 300% TIC for coated SBS folding carton. Files that exceed 300% risk ink set-off and blocking in the delivery stack, particularly in solid shadow areas. If your design has heavy coverage zones, we can advise on UCR (under-colour removal) settings before you finalise the file.

Q2: What is your standard lead time from approved artwork to production start?
A: Once we receive a file that passes preflight, we return a digital proof within 1–2 working days and a physical contract proof within 3–5 working days if required. Production lead time for folding carton is 15–20 working days after written proof approval — rigid box and flexible packaging runs are 20–28 working days.

Q3: Which colour standard do you use for press matching on coated substrates?
A: We use FOGRA 51 (ISO 12647-2:2013) as our characterisation dataset for coated offset work, and our sheet-fed offset lines are G7 Master certified. Press operators target a maximum ΔE of 2.0 against the approved proof under D50/2° observer conditions — this is the threshold at which colour difference becomes perceptible to a trained observer.

Q4: Can you handle files with both CMYK and Pantone spot colours on the same job?
A: Yes — we run up to 6-colour configurations on our Heidelberg XL 106, which accommodates 4-colour process plus 2 spot channels. Pantone references must be specified from the current Pantone+ Solid Coated or Solid Uncoated library. We apply a trap width of 0.10mm at the spot-to-CMYK boundary to manage register at the colour edge.

Q5: What happens if reversed-out text in my file is below your minimum size threshold?
A: Reversed-out text below 7pt is a hard-fail in our preflight — at standard offset ink viscosity (18–22 Pa·s), ink spread closes the counters of small reversed characters and the text becomes illegible on press. We flag this in our preflight report with the specific text elements and point sizes affected, and ask you to either increase the size or switch to a positive (dark on light) treatment before we proceed.

Planning a packaging project? Contact our team to request a complimentary specification review and sample quote.