Short answer
They can. Inks that bleed in the hot caustic wash tint the recycled plastic, inks printed directly on a bottle stay with the flake and can discolour it, and metallised decoration can confuse sorters or trigger metal separators. The effect depends on whether the ink is designed to stay on its label or wash off, where it is printed, and how much of the pack it covers.
Plastic bottles are ground into flakes and washed, usually in hot alkaline water. Labels and sleeves that float are skimmed off, and whatever ink is on them should go with them. An ink that dissolves or bleeds in that wash releases its colourant into the water, and the colourant can then stain the PET or HDPE flakes it meets. European PET guidance therefore prefers non-bleeding, retentive inks on labels and lists bleeding inks as not compatible; APR asks for inks on floating label substrates to resist hot caustic, and for inks on sinking labels to wash off without discolouring the wash water.
Printing directly on a bottle removes the label but puts ink straight onto the material being recycled. APR notes that hot-caustic-resistant inks printed directly on PET stay on the package and may cause discolouration of recycled PET, while wash-off inks can be removed from flake in the wash water and are preferred for direct print. European guidance is stricter: apart from laser marking and small production or expiry codes, it rates direct printing on clear PET bottles as not compatible. For colour, the implication is that large printed areas directly on a bottle are a recyclate-colour decision as well as a graphic one.
Metallic effects come from vacuum-metallised films, foils and metallic inks containing aluminium flake. In a sorting line, metal detectors and eddy-current separators remove metal to protect the process; a heavily metallised label can make a plastic bottle look like metal and send it the wrong way. APR requires metal decoration to be within its preferred coverage and tested, and treats untested or failing metal decoration as non-recyclable for PET. European guidance lists metallised labels, metallised sleeves and metallic inks as not compatible with clear PET, and lightly metallised floating labels as a limited option.
Coatings — varnishes, barrier layers, anti-fog or slip coatings — are usually thin and colourless, so their colour effect is indirect: some break down or yellow during reprocessing and add to the haze or tint of the recyclate. Opaque white coatings and pigmented barrier layers behave more like colourants, adding white pigment or other material to the stream. This is less documented in guidance than inks and labels, so the safe approach is to ask the coating supplier whether the coating has been tested with the relevant recycling protocol, rather than assuming a clear coating is neutral.
| Decoration choice | Process implication | Recyclate colour effect | Lower-impact alternative |
|---|---|---|---|
| Bleeding ink on label | Colour released in wash | Flake stained | Retentive, non-bleeding ink |
| Direct print, caustic-resistant ink | Ink stays on flake | Discolouration | Wash-off ink or label |
| Metallised label or sleeve | Metal detector may eject | Lost from stream | Light metallic ink area, tested |
| Metallic ink over large area | Sorting interference | Not compatible with clear PET (EU) | Printed metallic-look in non-metal ink |
| Laser mark or date code | Minimal | Negligible | — |
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.
ConventionModerate evidence· North America
Recycler guidance notes that hot-caustic-resistant inks printed directly on PET remain on the package and may cause discolouration of recycled PET, whereas wash-off inks can be removed from flake in the wash and are preferred for direct print.
Source: APR Design Guide for Plastics Recyclability: PET Rigid
ConventionModerate evidence· Europe
European PET bottle guidance rates non-bleeding, retentive label inks as fully compatible and bleeding inks, metallic inks, washable inks and most direct printing as not compatible with the clear bottle stream.
Source: RecyClass Design for Recycling Guidelines: Transparent Clear & Light-Blue PET Bottles; Design Guidelines for PET bottles
ConventionModerate evidence· North America
Metal decoration on PET labels must be tested for sortation under APR guidance; untested or failing labels with metal decoration are considered non-recyclable because of a higher probability of removal by the metal detector.
Source: APR Design Guide for Plastics Recyclability: PET Rigid
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.