Spot colors carry identity, warning, coding and decorative functions that CMYK builds may not reproduce reliably. Their control depends on spectral information and a physical print condition—not only a named swatch or three L*a*b* values. The target must describe the ink as it will appear on the intended substrate.
Define the complete standard
Use an approved spectral target or stable master print with a revision and owner. Record substrate, ink system, print process, film weight or anilox/plate condition, backing, ISO 13655 M condition, illuminant, observer and Delta E formula. If a color library is used, confirm that its substrate and measurement condition represent the job; the same color name on coated paper, uncoated board and clear film will not produce the same spectrum.
Produce a representative solid
Measure a uniform patch large enough to cover the aperture. For formulation drawdowns, control applicator, ink film, substrate lot, drying and backing. On press, allow the color to stabilise and sample across the web or sheet to expose lateral variation. Measure the final construction as well when varnish, laminate, reverse printing or a white underlayer changes appearance.
Solid ink is necessary but not always sufficient
A solid-patch match does not guarantee correct tint ramps, overprints or trapping. Add the process-control elements that matter to the design.
Measure and compare under one method
Verify the instrument, select the agreed M condition and backing, then average representative readings. Store the reflectance spectrum as well as colorimetric values. Use the specified Delta E formula and, where brand risk requires it, directional limits for lightness, chroma or hue. A low total difference can still conceal an objectionable hue shift.
Use color direction to diagnose the process
| Observed change | First checks |
|---|---|
| Too light or weak | Ink strength, film weight, viscosity, impression, anilox volume and substrate holdout. |
| Hue shift | Formula, contamination, pigment balance, drying, overprint and measurement condition. |
| Good press sheet, poor finished pack | Laminate, adhesive, varnish, white backing, heat history and final geometry. |
| Different result between sites | M condition, backing, aperture, instrument agreement, target revision and sample timing. |
Exchange data that another site can reproduce
ISO 17972-4 defines CxF/X-4 for spot-color characterisation data on paper-like substrates. Whatever file format is used, keep spectra and measurement metadata together. Validate borderline colors visually under the specified viewing condition and align the method with ISO 13655, print Delta E and the complete print and packaging guide.
Last reviewed 22/09/2026 · Level: Intermediate
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