Understanding Paint Pigments for Better Colour Mixing

Why Pigments Behave So Differently

Every tube of paint is a simple partnership: pigment, which supplies the colour, and binder, which holds it together and makes it spreadable. We tend to shop by hue name — ultramarine, burnt sienna, phthalo blue — but two tubes bearing the same name can feel utterly different on the palette. One may be buttery and opaque, the other thin and glassy. One may dry overnight; the other will still be tacky after a week.

Those differences come from the pigment itself. Particle size, particle shape and the way the pigment's surface reflects light all shape how a colour behaves when it meets the brush. Once you know what to look for, mixing stops feeling like guesswork and starts feeling like a conversation.

Opacity and Transparency

Some pigments hide what lies beneath them; others let it glow through. Opaque pigments — titanium white, the cadmiums, yellow ochre, Naples yellow — cover in a single confident stroke. Transparent ones — phthalo blue, quinacridone magenta, alizarin crimson, most of the modern organic reds — behave more like stained glass.

This matters twice over. First, it decides how you build up a painting: opaque colours for blocking in and covering, transparent colours for glazes and for deepening a passage without losing what sits underneath. Second, it decides how cleanly your mixtures read. Two transparent colours stirred together tend to keep their brightness; pile in an opaque white and you will lift the value but dull the chroma.

A quick test: brush a stripe of each colour across a strip of black and white card. Where it vanishes over black, it is transparent. Where it stays stubbornly itself, it is opaque. Keep the strip in your sketchbook — it will save you no end of muddled mixing.

Tinting Strength: How Far a Colour Stretches

Tinting strength is the measure of how much a pigment can be diluted before it stops dominating. Phthalo blue and the quinacridones are ferocious: a speck the size of a pinhead will tint an entire well of white. Earth colours — the ochres, umbers and siennas — are gentle by comparison, happy to be used generously.

The practical rule that follows is simple: always add the strong colour to the weak one, never the other way round. If you are mixing a pale sky, put your white out first and introduce the blue a touch at a time. Try to correct an over-strong blue by adding white and you will chase it around the palette until you have used half a tube.

Many painters keep a small note in the lid of their paintbox recording which colours are "one drop" pigments. It sounds fussy; it isn't. It is the difference between a mix you can repeat and one you will never find again.

Granulation, Staining and Sedimentation

If you work in watercolour, pigment behaviour in water matters as much as anything else. Staining pigments grip the paper fibres and refuse to lift — phthalo blue, the quinacridones and many modern reds are notorious for it. Once they are down, they are down. That is wonderful for vivid, permanent washes and slightly terrifying when you have made a mistake.

Granulating pigments do the opposite. Ultramarine, cerulean, viridian and raw umber settle into the troughs of rough paper, leaving a speckled, mineral texture. Used in a sky or a stone wall, that texture does half the work for you. Used in a smooth portrait, it can look gritty.

Drying Time and the Binder

In oils, drying is a chemical conversation between the binder and the pigment. Some pigments hurry it along — raw umber and burnt sienna are traditionally the quickest of the earths — while others hold it back. Titanium white and many of the cadmiums are slow, and a few organic pigments can leave a layer tacky for days.

This is why a painting made entirely of slow-drying colours can remain soft for far longer than you expect, and why an underpainting of fast-drying earths gives you a stable surface to work over. In watercolour and acrylics the binder drives drying, but pigment still shapes how much water you need and how evenly a wash settles.

Keep a small record: a dab of each colour on a scrap of board, with the date you painted it. After a season you will have a personal drying chart worth more than any printed one.

A Simple Routine for Confident Mixing

• Mix with a knife, not a brush. Brushes trap pigment in the ferrule and contaminate your next colour.
• Start small. Take a little of the weaker colour, then introduce the stronger one in increments, checking against your reference as you go.
• Test on scrap. A mix looks different wet on the palette and dry on the surface. Paper or board offcuts are cheap; repainting is not.
• Write down ratios. If a mix sings, note roughly how many parts of each you used. Memory is a poor record-keeper.
• Accept the odd surprise. Some pigments shift hue as they dry, and some pairings of complementary colours will always turn towards grey. Knowing why is usually enough.

None of this requires expensive kit or a chemistry degree. It simply asks you to pay attention to the materials in front of you — and to treat every failed mix as information rather than waste.