Pigments and Colour Matching
Pigments and Colour Matching
This domain tests pigment types and properties, and the practical steps of matching a colour. Questions often compare hiding power, tinting strength or lightfastness.
Pigment classes and properties
- Inorganic pigments include titanium dioxide, iron oxides, zinc phosphate and zinc dust. They are generally opaque, stable and lightfast.
- Organic pigments are often brighter and stronger but vary in lightfastness and bleed resistance.
- Extenders such as calcium carbonate, talc and barytes add bulk and control gloss and sanding.
- Hiding power is the ability to obscure the substrate; tinting strength is the ability to colour a white or base paint.
- Oil absorption affects binder demand and viscosity.
- Bleeding pigments dissolve in solvent and stain the topcoat; lightfast pigments resist fading.
- Some pigments contain lead or chromate and carry health controls.
Colour matching sequence
Identify the base, add the strongest colour in small increments, check under the specified light, and record the formula by weight. Strong tinters such as phthalo blue are added last and in tiny amounts.
Worked example
Two yellow pigments are compared by mixing 1 g of each into 10 g of white base. Pigment A gives a deeper, stronger tint than pigment B. Pigment A has higher tinting strength, so less is needed to match a given colour. The reasoning is that tinting strength is measured by the colour produced per unit mass in a standard white.
Traps
- Adding a strong tinter first and overshooting the match.
- Judging hiding power on a thin drawdown rather than at the specified film thickness.
- Using a bleeding pigment under a white topcoat.
- Ignoring pigment toxicity and spray controls.