A tube labelled Yellow Ochre may sound self-explanatory, but its colour name alone does not tell you what is inside. It may be made with natural earth, synthetic iron oxide, or a blend designed to resemble a familiar hue. Learning how to read pigment codes gives you a more reliable way to choose paint: by the material that creates the colour, rather than by the name on the front of the tube.

For painters building a considered palette, this small piece of label knowledge has practical consequences. It helps you predict mixing behaviour, recognise genuine equivalents between ranges, avoid unnecessary duplication and make better decisions about permanence, opacity and value.

What a pigment code tells you

Most professional paint labels include a Colour Index name or pigment code. This internationally recognised system identifies the pigment or pigments used in a colour. A code usually begins with two letters indicating the colour family, followed by a number identifying the particular pigment.

For example, PB29 is Pigment Blue 29, commonly known as Ultramarine Blue. PR108 is Pigment Red 108, Cadmium Red. PY42 is Pigment Yellow 42, an iron oxide yellow often used for Yellow Ochre and related earth colours.

The letters are a useful first indication of the pigment family:

• PY means Pigment Yellow
• PR means Pigment Red
• PB means Pigment Blue
• PG means Pigment Green
• PV means Pigment Violet
• PBr means Pigment Brown
• PO means Pigment Orange
• PW means Pigment White
• PBk means Pigment Black

The number matters just as much as the letters. PB15 and PB29 are both blue pigments, for instance, but they have very different characters. PB15, Phthalo Blue, is generally powerful, staining and capable of intense clean mixtures. PB29, Ultramarine Blue, is softer in tinting strength, often granulating in watercolour, and tends towards warmer violet-leaning mixtures. “Blue” is not enough information when you are choosing a mixing blue.

How to read pigment codes alongside colour names

Colour names are useful shorthand, but they are not a universal formula. One manufacturer’s Naples Yellow may differ substantially from another’s. A colour called Permanent Alizarin Crimson may contain a modern quinacridone, a naphthol red, or a blend of several pigments. Neither option is automatically better. The question is whether the paint behaves as you need it to behave.

Read the name first as an invitation, then check the pigment code as the evidence. If a colour is labelled Burnt Sienna and contains PBr7, you are looking at an earth pigment family. If another Burnt Sienna contains PR101, it is based on synthetic red iron oxide. These pigments can produce closely related hues, yet their undertones, transparency, texture and response in mixtures may differ.

This is particularly useful when replacing a familiar colour. Instead of searching solely for the same name, compare the pigment code, transparency and colour bias. A like-for-like pigment is usually the soundest starting point, although paint-making choices such as particle size and binder still affect the final handling.

Single-pigment colours and mixtures

When a label carries one pigment code, such as PV19 or PG7, the paint is a single-pigment colour. These colours are often valued for clarity in mixing. Because there is only one colourant present, their contribution to a mixture is easier to anticipate. They can be especially useful when constructing a compact palette or correcting a mixture without introducing an unexpected third hue.

A label with two or more codes identifies a mixture. For example, a convenience green may include PY3 and PG7, while a warm grey may combine a blue, red and black pigment. Mixed-pigment colours are not inferior materials. They can be beautifully balanced, economical in the studio and difficult to reproduce quickly from a limited palette.

The trade-off is control. Each added pigment brings another bias to a mixture. A pre-mixed green may be ideal for a specific landscape passage, yet repeated additions of red, blue and yellow blends can make greys and darks less predictable. If your work depends on clean secondaries or restrained neutral passages, understanding the pigments in convenience colours becomes increasingly valuable.

When a mixture is the better choice

There is no rule that a serious painter must use only single-pigment colours. A carefully made mixture can offer a particular undertone, body or granulating effect that would take several paints to achieve. In watercolour, a two-pigment earth or green may produce lively separation across textured paper. In oil, a prepared flesh tone or neutral can support speed and consistency across a large painting.

Choose single-pigment colours when maximum mixing clarity is the priority. Choose mixtures when their specific visual character earns a place on the palette.

Pigment codes do not tell the whole story

A pigment code is essential information, but it is not a complete description of a paint. The same pigment may feel different across oil colour and watercolour, or between manufacturers using different grades, particle sizes and pigment concentrations.

In watercolour, look at granulation, staining and transparency as well as the code. PB29 will often granulate, but the degree of granulation depends on formulation and the paper beneath it. In oil colour, consider tinting strength, drying characteristics, opacity and the way a pigment handles under the brush or knife. Earth pigments can feel dense and responsive, while some modern organic pigments are exceptionally strong and transparent.

The binder also changes the experience. Gum arabic allows watercolour pigment to re-wet and travel through washes; linseed oil gives oil colour body, depth and a different refractive quality. A pigment code identifies the colourant, not every aspect of the finished paint.

Use codes to judge permanence and safety

Professional labels normally provide permanence information separately, often through a rating system. Do not assume that all pigments within a colour family have the same lightfastness. Historical pigments and names can be especially misleading here. A modern paint bearing a traditional name may be formulated with a more permanent alternative, which is often a sensible choice for work intended to endure.

Pigment codes can also help you identify colours requiring particular studio care. Cadmium pigments, commonly identified by codes including PY35, PO20 and PR108, are valued for their opacity and distinctive colour, but artists should handle all dry pigments and paint residues responsibly. Good studio practice includes avoiding airborne dust, keeping materials away from food preparation, and following local guidance on disposal.

The code alone does not establish whether a paint is non-toxic or suitable for a particular practice. Refer to the full label, safety information and any clear vegan or non-toxic designation supplied by the manufacturer. Material knowledge is most useful when it informs sensible working habits rather than creating unnecessary anxiety.

A practical way to compare two tubes

When choosing between similarly named paints, begin with the pigment line. If both tubes contain the same single pigment, compare their stated opacity, permanence and the format you use. Then make a small test rather than relying on a colour chart alone.

In watercolour, paint a full-strength swatch, pull it into a graded wash and mix it with one warm and one cool counterpart. Observe how it settles, stains and lifts once dry. In oil, make a masstone swatch, a tint with white and a few controlled mixtures. This reveals whether the colour leans warmer or cooler than expected, and how quickly it dominates another pigment.

Keep these tests in a notebook with the pigment codes written beside them. Over time, the codes stop feeling technical and become a useful studio language. You will recognise that a favourite transparent red contains PR122, or that two apparently different greens share PG7 as their strongest component.

How to read pigment codes when building a palette

A palette built only by colour names often accumulates near-duplicates. A palette built with pigment codes in view can remain leaner and more intentional. You may find you already own several paints based on the same high-strength blue, or that your warm and cool reds are all mixtures with similar underlying biases.

Start by grouping your existing paints according to pigment family, then identify which pigments you actually use most. For a limited palette, aim for distinctions that matter: a cool staining blue and a warmer granulating blue; an opaque warm yellow and a transparent cool yellow; an earth red alongside a high-chroma modern red. The exact selection depends on your subject, medium and working method.

Michael Harding colour information is designed to support this level of choice, so that the colour in your hand is not simply named, but understood. A pigment code will never dictate a painting. It gives you a firmer point of reference, leaving your eye and your experience free to make the final decision.