Short answer
Recovered paper is pulped in alkaline water to loosen the ink, then ink particles are removed mainly by flotation — air bubbles carry them to a froth that is skimmed off — with washing and bleaching as further steps. How well a printed product deinks depends on the ink, the paper and the print process, and in Europe it is assessed with a laboratory test scored on brightness, colour shade, dirt specks, ink removal and filtrate darkening.
Deinking starts by turning recovered paper into a slurry in warm alkaline water, usually with hydrogen peroxide added to counter the yellowing that alkali causes in mechanical-pulp fibres. Mechanical action and chemistry detach ink films from the fibres and break them into particles. Particle size matters for everything that follows: particles that are too large stay visible as specks, and particles that are too small behave like fines and are hard to separate. Inks that are well suited to deinking break up into particles of a size the process is designed to remove; some modern inks and toners do not.
In flotation, air is blown through the diluted pulp with a surfactant or soap. Hydrophobic ink particles attach to the bubbles and rise into a froth that is skimmed off, while the fibres stay in suspension. Flotation is effective for mid-sized ink particles. Washing removes very small particles and fillers by draining water through the fibre mat, at the cost of some fibre and filler loss. INGEDE's standard laboratory method deliberately simulates alkaline pulping plus flotation only — leaving out dispersion, post-flotation, washing and bleaching — so that it tests the printed product rather than the mill's full line.
The European Paper Recycling Council's scorecard converts the results of INGEDE Method 11 into a score. It weights five things: the luminosity (Y) of the deinked pulp, its colour shade on the a* axis, the area of dirt specks in two size classes, how much ink was eliminated, and how much the filtrate is darkened. Each parameter has a threshold that must be met and a target for full points; luminosity carries the most weight. A product scoring 71–100 is rated good and 51–70 fair; in the 2017 issue, 0–50 is rated tolerable. If any parameter fails its threshold, the product is rated not suitable for deinking, though it may still be recyclable in grades that are not deinked.
Deinking removes ink; it does not remove the yellowness of lignin-containing fibres or dyes inside the fibres. Mills therefore bleach deinked pulp with oxidative agents such as hydrogen peroxide, reductive agents such as sodium dithionite or formamidine sulphinic acid (FAS), or both in sequence. The USDA Forest Products Laboratory reported that reductive agents strip many paper dyes and that FAS stripped a larger share of the dyes then in use than dithionite. In a 2018 study of mill deinked pulp, an oxidative stage followed by a reductive stage raised brightness by more than nine points, more than either agent alone or the reverse order.
| Pulp | Unbleached (% ISO) | Peroxide (% ISO) | Dithionite (% ISO) |
|---|---|---|---|
| High-grade furnish | 70 | 75.5 | 73.8 |
| Ordinary-grade furnish | 58 | 62.1 | 61.5 |
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· Europe
The ERPC deinkability score is derived from INGEDE Method 11 and weights luminosity, a* colour shade, dirt area in two size classes, ink elimination and filtrate darkening, with luminosity carrying the largest share of points.
Source: Assessment of Printed Product Recyclability – Deinkability Score (Issue 2); INGEDE Methods – to evaluate Recyclability and Deinkability
StandardModerate evidence
In the 2017 issue of the ERPC scorecard, scores of 71–100 are rated good, 51–70 fair and 0–50 tolerable, and a product failing any parameter threshold is rated not suitable for deinking.
Caveat: Band names have changed between issues of the scorecard.
Source: Assessment of Printed Product Recyclability – Deinkability Score (Issue 2)
FactStrong evidence
In bleaching two mill deinked pulps, a peroxide stage followed by a dithionite stage raised ISO brightness by about 9–10 points, more than the reverse sequence or either agent alone at the same total charge.
Caveat: Two tissue-grade pulps from one mill.
FactModerate evidence
Reductive bleaching agents such as FAS and sodium dithionite can strip many paper dyes from recycled fibre, with FAS reported to strip a larger share than dithionite.
Caveat: 1992 assessment of the dyes then in use.
Source: Recycling Bleach Technologies
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.