Short answer
On coated paper the ink film stays on a smooth, closed surface, so solids are dense and saturated and dots stay sharp. On uncoated paper ink soaks into fibres and the rough surface scatters light, so blacks are lighter, colours less chromatic and tones darker through dot gain. In the published offset data the black solid is about L* 16 on coated against 33 on uncoated, and the blue overprint loses over a third of its chroma.
A coated paper has a layer of mineral pigment and binder — typically clay or calcium carbonate — applied and often calendered to a smooth finish. Ink placed on it sets at the surface with little penetration, so the full film thickness contributes to colour and the dot keeps its edge. Uncoated paper is a web of cellulose fibres with sizing; ink vehicle wicks into the fibres and takes pigment with it, the surface is rough enough to scatter white light back from within and around the ink, and dots spread. Each of those effects lightens dark colours and greys out saturated ones.
The table compares every patch of the two current European offset conditions: premium coated (FOGRA51) and wood-free uncoated (FOGRA52). Paper white is similar in lightness but the uncoated sheet is more heavily brightened. The black solid is about 17 L* units lighter on uncoated; the three-colour overprint is over 11 units lighter. Every chromatic solid and overprint loses chroma, the blue and green overprints most. The CIEDE2000 column shows the colour difference a designer would see if a file separated for one were printed on the other without re-separation: the black solid and blue overprint differ by about 12 ΔE00 and most other patches by 4 to 9.
Uncoated paper does not only lower the ceiling on saturation; it raises tone value increase. A 50 % dot spreads further into fibres and scatters light beneath its edge (optical dot gain), so mid-tones print darker than on coated stock. ISO 12647-2 assigns the uncoated paper class a different tone value increase curve (curve C) from premium coated (curve A) for this reason. A file separated for coated paper and printed on uncoated therefore looks both duller and heavier — the classic 'muddy' print.
Uncoated paper is chosen for its feel, writability and look, and those are real advantages; it just needs its own separations. Use the uncoated profile from the start so the soft proof shows the real result. Avoid relying on deep, saturated blues or large rich blacks, which uncoated stock cannot deliver. Open up shadows slightly in images. For brand colours, specify spot inks with uncoated swatch references — ink manufacturers publish separate coated and uncoated guides for exactly this reason — rather than expecting the coated appearance.
| Patch | Coated L* / C* | Uncoated L* / C* | ΔE00 between them |
|---|---|---|---|
| Paper white | 95 / 6.2 | 93.5 / 10.3 | 3.2 |
| Cyan (C) | 56.12 / 63.1 | 58.7 / 53.1 | 5.5 |
| Magenta (M) | 48.06 / 75.5 | 54.54 / 60.2 | 7.5 |
| Yellow (Y) | 88.94 / 92.5 | 87.66 / 72.4 | 4.3 |
| Black (K) | 16 / 0.3 | 32.69 / 1.2 | 12.2 |
| Red overprint (M+Y) | 47.99 / 83.1 | 52.59 / 61.5 | 9.1 |
| Green overprint (C+Y) | 49.45 / 70.3 | 51.97 / 42.9 | 8.5 |
| Blue overprint (C+M) | 24.74 / 51.9 | 38.47 / 33.4 | 11.9 |
| Three-colour overprint (C+M+Y) | 23.26 / 2.2 | 34.61 / 4.3 | 9.4 |
Why: Separated for coated paper: too much ink and no allowance for uncoated dot gain.
Fix: Re-separate with an uncoated profile; soft-proof with it before approving.
Why: The target lies outside the uncoated gamut.
Fix: Approve a separate uncoated target or use an uncoated spot-ink reference.
Each statement is labelled by kind — established fact, a standard’s requirement, observed market data, a convention, or Colourwise’s own interpretation or analysis — with the strength of the evidence behind it.
FactStrong evidence
In the published offset characterisation data, the black solid is L* 16.0 on premium coated paper (FOGRA51) and L* 32.7 on wood-free uncoated paper (FOGRA52), and the blue overprint's CIELAB chroma is about 52 against about 33.
Caveat: Chroma values computed from the published a* and b*.
Source: FOGRA51 characterization data (premium coated offset, ISO 12647-2:2013); FOGRA52 characterization data (wood-free uncoated offset, ISO 12647-2:2013)
StandardStrong evidence
ISO 12647-2:2013 assigns tone value increase curve A to the premium coated printing condition and curve C to the uncoated printing condition.
Source: ISO 12647-2:2013 Graphic technology — Process control … — Part 2: Offset lithographic processes; FOGRA52 characterization data (wood-free uncoated offset, ISO 12647-2:2013)
Colourwise analysisStrong evidence
Between the FOGRA51 coated and FOGRA52 uncoated conditions the black solid and the blue overprint differ by about 12 ΔE00, and every other chromatic solid and overprint by roughly 4 to 9 ΔE00.
Based on: CIEDE2000 computed by Colourwise between corresponding patches of the two data sets; see the table.
Source: FOGRA51 characterization data (premium coated offset, ISO 12647-2:2013); FOGRA52 characterization data (wood-free uncoated offset, ISO 12647-2:2013)
Reviewed 29 September 2026. Colourwise summarises its sources in its own words and does not reproduce standards text or proprietary colour data. Spotted an error? Tell us.