A tube labelled Naples Yellow, Rose Madder or Permanent Green tells only part of the story. An oil paint pigment index guide takes you to the information that matters in the studio: the pigments present, their Colour Index names and numbers, and the likely character of the paint on the palette and in a mixture.
For painters who want greater control, this small line of technical information is not an administrative detail. It can explain why two colours with similar names mix very differently, why one version covers beautifully while another glazes, or why a familiar favourite is no longer the right choice for a particular painting.
What the pigment index tells you
The pigment index usually refers to the Colour Index system, a shared classification that identifies a pigment by both its colour family and its specific number. You may see a code such as PB29, PR122 or PY43 on a paint label.
The letters identify the colour family: P means pigment, followed by B for blue, R for red, Y for yellow, G for green, O for orange, V for violet, Br for brown, W for white and Bk for black. The number identifies the particular pigment within that family. PB29, for example, is Ultramarine Blue; PR122 is Quinacridone Magenta; PY43 is Yellow Ochre.
A Colour Index code does not tell you every aspect of a paint's formulation. It will not state the proportion of pigment, the grade of linseed oil, or precisely how the colour has been milled. Those things matter greatly to handling and strength. But it gives you a dependable starting point for comparing colours across a palette, especially when product names are historical, poetic or used differently by different makers.
How to read an oil paint pigment index guide
Start with the pigment code, then look at the number of pigments listed. A single-pigment colour contains one identified pigment, such as PB29 in Ultramarine Blue. A mixed-pigment colour might contain several codes, perhaps a yellow, a blue and a white, to create a particular green or a lighter convenience mixture.
Neither is automatically superior. Single-pigment colours are often easier to predict when mixing because their undertone and behaviour are easier to isolate. They are particularly useful when building a restrained palette, matching a colour from observation, or learning the relationships between pigments.
Mixed-pigment colours can be genuinely valuable, however. They may provide a carefully balanced hue that would take time to mix repeatedly, or a useful, stable alternative where a historic pigment is unsuitable. The question is not whether a colour is pure, but whether its composition serves the painting you are making.
The code is more reliable than the name
Traditional colour names can refer to very different materials. “Alizarin Crimson” may indicate a fugitive historical lake pigment in one context, while “Permanent Alizarin Crimson” may be a modern blend of more lightfast pigments. “Indian Yellow” can be formulated from a variety of modern yellow and orange pigments. “Viridian Hue” is not necessarily Viridian.
Read the pigment line before assuming that two similarly named paints are equivalents. If their Colour Index codes differ, expect differences in hue, tinting strength, transparency, drying behaviour and mixtures. A name tells you an intention or a tradition; the pigment index tells you what is actually in the tube.
One pigment does not mean one result
Even when two paints share the same Colour Index code, they are not necessarily interchangeable. Pigment particle size, concentration, milling and the oil vehicle affect consistency, gloss, brush drag and colour strength. One version of a pigment may feel short and dense, another more fluid or more transparent in a thin film.
This is why the pigment index should guide comparison rather than replace practical testing. Make a drawdown, paint a tint with a consistent white, and mix the colour with the pigments most used in your work. The evidence on your palette is the final test.
Use the index to anticipate mixing behaviour
The most useful habit is to connect pigment information with what happens in paint. Broadly, organic pigments such as quinacridones and phthalocyanines often offer high chroma and transparency. Earth pigments, including ochres, siennas and umbers, tend towards quieter mixtures, lower tinting strength and dependable naturalistic colour. Mineral pigments can bring distinctive texture and granularity of colour, even in oil.
These are tendencies, not rules. A pigment's behaviour depends on its particular formulation and on the colours beside it. Still, recognising pigment families helps you make more informed choices.
Consider a green landscape mixture. A bright green made with a phthalocyanine blue and a high-chroma yellow may be intense, staining in character and difficult to mute without introducing a complementary or earth colour. A green made from an earth yellow and Ultramarine Blue will usually be quieter and easier to steer towards greys and olive notes. Both mixtures may be useful. The subject, light and desired surface all determine which is appropriate.
The pigment index also makes it easier to avoid accidental over-complexity. If a convenience green already contains three pigments, then adding it to a mixture of several other composite colours can quickly produce mudded, difficult-to-repeat results. This does not prohibit blends. It simply asks you to know when you are using one.
Opacity, transparency and lightfastness
A pigment code alone cannot fully describe opacity, transparency or permanence, so read these alongside the index. These properties answer different questions.
Opacity tells you how readily a colour covers what lies beneath. Opaque colours are useful for decisive passages, corrections, body colour and planes where you want a solid statement. Transparent colours are often favoured for glazing, optical depth and allowing a lower layer to remain active. Semi-opaque colours sit between the two and can be among the most versatile paints in a palette.
Lightfastness concerns how well a pigment resists change under light exposure. For work intended to last, this should be a primary selection criterion, particularly with bright reds, violets and some historical colour names. A paint may be beautiful in the moment yet unsuitable for a painting expected to retain its colour over decades.
Drying rate is another practical consideration. Earth colours and lead-based whites generally dry more readily than some slow-drying modern organic pigments. If you work wet into wet, differing drying speeds can be helpful or inconvenient. If you glaze in layers, they become part of the painting schedule. The pigment index will not solve this question on its own, but it gives useful clues when combined with a maker's technical information and your own tests.
Build a palette from functions, not tube names
Rather than collecting colours because their names sound useful, choose pigments that perform distinct roles. A compact oil palette often benefits from a warm and cool yellow, a warm and cool red, a blue with suitable mixing range, an earth red or yellow, a transparent dark and a white. The exact selection depends on your subjects and method.
For portraiture, an earth-led group might matter more than an exceptionally vivid green. For florals or contemporary high-chroma work, transparent quinacridones and phthalocyanine colours may earn their place. A painter working in direct, opaque passages will select differently from one relying on layered glazes.
When considering a new tube, ask three practical questions. Does it contain a pigment already represented in the palette? Does it solve a recurring mixing problem? Can its behaviour be replicated by colours you already own? If the answer to the last question is yes, it may still be worth having for speed, but it is a convenience rather than a necessity.
A considered range of single-pigment colours is often the clearest foundation. From there, add mixed-pigment convenience colours deliberately, where they suit your working rhythm and visual language.
Keep a pigment record in the studio
The most effective pigment index guide is one you test and annotate. Paint each colour in mass tone, reduce it with white, and make small mixtures with the key colours in your palette. Record the Colour Index code, transparency, drying observations and any notable shifts in undertone.
Over time, this becomes more useful than a generic colour chart because it reflects your own brushes, grounds, medium use and subjects. It also makes replacement decisions simpler. If a tube runs out, you can identify whether you need the same pigment, the same hue, or merely the same function in a mixture.
Michael Harding oil colours are made with this kind of material awareness in mind: pigment identity is a starting point for a more exact relationship with colour, not a substitute for painting.
Next time a colour catches your attention, turn the tube over before placing it in the basket. Read the pigment index, imagine the mixtures it will make, then let a small studio test decide whether it has earned a permanent place on your palette.