Short answer
Tinting strength is how much a colourant changes a white (or another colour) per unit added. It is measured by letting the colourant down in a standard white and comparing the result with a reference, and it follows from how much light the colourant absorbs relative to how much the mixture scatters. Strong colourants — phthalocyanine blues and greens, carbon black, many modern organics — shift a mixture a long way for a small addition; weak ones, such as many earths, need several times as much.
In an opaque paint the absorption and scattering coefficients of the components add, each weighted by its concentration, and the colour of a thick film depends only on the ratio of the totals, K/S. A white contributes a large S and almost no K. A colourant contributes its own K and usually a smaller S. Adding a colourant therefore raises K/S, and reflectance falls — quickly at first, then more slowly, because reflectance is a curved function of K/S. That curvature is why the first few drops of a strong colour in white change it dramatically while doubling an already strong mix changes it little. Colour-matching software works by exactly this additivity, applied at every wavelength rather than one.
The table compares two illustrative colourants let down in the same white: one with high absorption and little scattering, typical of fine organic pigments, and one with lower absorption and more scattering, typical of many inorganic pigments. At 1% the strong colourant takes the mixture from near-white to a reflectance of about 64%; the weak one only to about 82%. To match the strong colourant's reduction, the weak one is needed at about five times the concentration in this example. That ratio — how much of one product is needed to equal another — is what a relative tinting strength figure expresses, usually as a percentage against a reference batch.
For manufacturers, tinting strength is money: colourant is priced by weight but sold by effect, so a batch 10% weaker than standard needs 10% more in every formulation. It is also a quality check, because strength drops when a pigment is poorly dispersed or has flocculated. For painters and decorators it is about control. A very strong colourant is efficient but unforgiving: a mix meant to be a pale blue can go mid-blue with one careless addition, and the strong colour dominates any mixture it enters. Titanium white is itself strong in this sense — it lightens other colours more per gram than lead or zinc white, which is why titanium-white tints can look chalky if white is added in large steps.
Strength also explains why a colour looks different in the tin and in a tint. A strong, transparent colourant used alone gives a dark, sometimes almost black masstone, because it absorbs nearly everything over the depth of the film; only when let down with white does its hue show clearly — its undertone or tint tone. Two pigments with near-identical masstones can separate sharply when tinted, one leaning warmer and one cooler, which is why pigment makers and paint mixers compare products in a let-down with white rather than neat. The same logic is behind the colour-mixing guidance elsewhere on this site: judge a mixing colour by its tint, not its masstone.
| Colourant in the mix | Strong colourant (K 40, S 0.4) | Weaker colourant (K 8, S 3) |
|---|---|---|
| 0.5% | 72.7% (L* 88) | 86.2% (L* 94) |
| 1.0% | 63.9% (L* 84) | 81.5% (L* 92) |
| 2.0% | 53.3% (L* 78) | 75.1% (L* 89) |
| 5.0% | 37.4% (L* 68) | 63.9% (L* 84) |
| 10.0% | 25.3% (L* 57) | 53.2% (L* 78) |
| 20.0% | 14.9% (L* 45) | 41.1% (L* 70) |
| Strong colourant | Weaker colourant needed for the same K/S | Ratio |
|---|---|---|
| 0.5% | 2.5% | 5.0× |
| 1.0% | 5.0% | 5.0× |
| 2.0% | 9.9% | 5.0× |
| 5.0% | 24.6% | 4.9× |
Why: The colourant has high tinting strength and the white is near the steep start of the K/S curve.
Fix: Pre-dilute the strong colour into some of the white, then add that mixture gradually.
Why: The new colourant batch is weaker or less well dispersed than the previous one.
Fix: Compare the colourants in a standard let-down against a retained reference before mixing, and adjust quantities.
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.
Colourwise analysisLimited evidence
In an illustrative single-wavelength Kubelka–Munk model, a strongly absorbing, weakly scattering colourant lowers a white's reflectance to about 64% at 1%, while a weaker, more scattering colourant needs about five times the concentration to give the same reduction.
Based on: Colourwise calculation with additive K and S mixing and R∞ = 1 + K/S − √((K/S)² + 2K/S); coefficients stated in the table notes.
Caveat: Illustrative coefficients at one wavelength; real products need measured spectral K and S.
Source: New Contributions to the Optics of Intensely Light-Scattering Materials. Part I (Journal of the Optical Society of America, 1948); Kubelka–Munk theory
FactModerate evidence
Titanium white has higher tinting strength than earlier white pigments such as lead white and zinc white.
Source: Titanium white
FactStrong evidence
Commercial products listed under the same Colour Index Generic Name may not have identical application or fastness properties, so pigment identity alone does not fix a product's strength or behaviour.
FactModerate evidence
Colourants in an opaque film combine approximately by adding their absorption and scattering coefficients weighted by concentration, which is the basis of instrumental colour matching.
Caveat: Breaks down for transparent films, strong surface effects and interacting pigments.
Source: New Contributions to the Optics of Intensely Light-Scattering Materials. Part I (Journal of the Optical Society of America, 1948); Kubelka–Munk theory
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.