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.
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:
| Substrate | Max TIC (%) | Reason |
|---|---|---|
| SBS folding carton (coated) | 300% | Prevents ink set-off and blocking in delivery |
| Uncoated kraft / recycled board | 260% | Limits ink absorption bleed and mottle |
| Flexible film (gravure) | 280% | Avoids ink cracking on flex and lamination adhesion loss |
| Rigid box wrap paper (coated art) | 320% | Higher tolerance due to slower press speed |
| Digital (HP Indigo / toner) | 220% | Toner adhesion limit on coated substrates |
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:
| Trap scenario | Trap width | Direction |
|---|---|---|
| Colour-to-colour (similar lightness) | 0.10–0.15mm | Spread lighter into darker |
| Colour-to-white (knockout) | 0.15–0.20mm | Spread colour |
| Black text on colour background | Overprint (no trap) | N/A |
| Spot colour to CMYK | 0.10mm | Spread spot into CMYK |
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.
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The 300% TIC limit on SBS coated is accurate but we’ve had jobs where the brand’s design agency delivered files at 340%+ on a shadow-heavy background panel and the prepress team didn’t catch it until we were already 2 days into a 12-day production window for a retailer launch — that recovery time basically doesn’t exist.
The 260% TIC cap on recycled kraft we run at our Łódź facility actually helped push us toward a cleaner ink set overall — we’d been running dense coverage blacks that were borderline anyway, and reformulating to stay under threshold meant we could finally hit the APR recyclability protocols our retail partner had been asking about for two years.
The RGB-to-CMYK conversion point is one we push back on constantly — had a cosmetics client submit a hero burgundy in RGB last spring and the D50-corrected proof came back looking closer to terracotta, took three rounds of approval to get brand sign-off.
Watch the flexible film TIC spec carefully if you’re running a white ink base layer underneath process colours — that 280% ceiling doesn’t account for the white, and on reverse-printed BOPP we’ve seen delamination at the seam area when total laydown including white hit closer to 340%.
The font embedding point isn’t mentioned much in these comments but it’s where we’ve had the most back-and-forth with smaller brand partners — specifically around variable fonts, which Acrobat’s preflight profile flags differently depending on the PDF version. PDF/X-1a won’t accept them at all, but we’ve had files submitted as PDF/X-4 where the variable font technically passed the embedding check and still caused glyph substitution on our RIP because the instance wasn’t flattened before export.
Overprint behaviour is the one that catches people out most on coated vs uncoated substrates — on 350gsm GC1 folding carton the ink sits on the surface long enough that a misset overprint on a black keyline over a spot colour reads as a visible knockout artifact, whereas on uncoated recycled board the ink penetration is aggressive enough that the same error sometimes self-corrects visually because both inks are already diffusing into the fibre. Doesn’t mean you let it through, but the failure mode looks completely different depending on which line the job’s going to.
Curious whether the 300% TIC cap on SBS accounts for aqueous coating applied inline — we’ve had folding carton jobs on 350gsm GC2 where the flood coat effectively seals the ink before set-off becomes an issue, and the prepress team has pushed back on rejecting files at 310-315% on that basis.