Created in 1925, the Colour Index International is a database of pigments and dyes published by the Society of Dyers and Colourists and the American Association of Textile Chemists and Colorists. Colourants are given many different proprietary and generic names, but the Colour Index International provides a standardised system used by manufacturers and consumers all over the world that can be a hugely informative tool for artists.
What is a Pigment?
Pigments are fine coloured powders that can be mixed with a binder – such as linseed oil, gum arabic, or acrylic polymer – to make artist paints. While dyes are soluble and dissolve in the binding medium (enabling them to chemically bind with a material – ideal for colouring textiles), pigments are insoluble and are suspended within the binding medium. The manufacture of artist paints consumes a tiny fraction of the pigment industry – the vast majority of pigments are used in larger industries, like in the production of cars and plastics.
Pigment being mixed with linseed oil at Michael Harding.
How Does the Colour Index Work?
Unlike other colour systems, like Pantone or the Munsell System, the Colour Index International groups dyes and pigments according to their chemical composition rather than the exact hue, value, and chroma of the colour they produce.
Each pigment entry has two identifying codes – the Colour Index Constitution Number, and the Colour Index Generic Name Code. For example, Ultramarine Blue is categorised under CI 77007 (the Colour Index Constitution Number) and PB 29 (the Colour Index Generic Name Code). The Colour Index Generic Name Code is most recognisable to artists, and it’s common to find one or more of these codes listed as part of the colour description before you choose it, and on the tube or bottle of paint:
A tube of Ultramarine Blue Williamsburg Oil Paint.
The letters classify the colour group, e.g. PB= Pigment Blue, PW= Pigment White, PV= Pigment Violet, etc. The number classifies the chemical composition – so PB 29 can be read as ‘Pigment Blue 29’ – identifying it as sodium-aluminium-sulpho-silicate, or Ultramarine Blue (like on the Williamsburg tube above, some manufacturers add the chemical formula alongside the Colour Index Name Code, but not all do). The number is not related directly to any part of the actual chemical structure, rather they are assigned chronologically in order of when the pigment was added to the index (not when the pigment was discovered).
Paint manufacturers are not obliged to disclose what pigments are in their paints. Some pigment mixtures, like Winsor & Newton’s Cadmium-free colours, are proprietary and the Colour Index Codes aren’t given. Most paint ranges, particularly professional ones, do include them on the label.
Why is the Pigment Colour Index Useful for Artists?
Here are some of the reasons why it can be so useful to become familiar with the Pigment Colour Index:
1. The Pigment Colour Index Provides Insight Into How Different Paints Behave
All pigments have individual characteristics including transparency/opacity, tinting strength, granulation (in watercolour), drying rate, lightfastness, and permanence – all of which huge impact on your painting. These pigment properties are determined by their physical attributes and chemical structure, and while the exact science behind this is complex, knowing how certain pigments behave is a great way to get the most from your artist paints.
A selection of yellow pigments, all with different properties
2. Colour Names Are Not Always Reliable
You can’t always rely on the name of the colour. As an example, here are the pigments used in a selection of paints labelled ‘Naples Yellow’, a historical toxic pigment that is often recreated for the modern artist using a mixture of pigments. Similar to food ingredients labels, pigments are usually listed in order of predominance (the pigment used in the greatest amount first, followed in descending order by those in smaller amounts).
- PW 6 (Titanium White), PY 42 (Synthetic Yellow Iron Oxide) – Old Holland New Masters Acrylic Paint
- PW 4 (Zinc White), PW 6 (Titanium White) , PY 35 (Cadmium Yellow) – Sennelier Watercolour Paint
- PW 4 (Zinc White), PY 35 (Cadmium Yellow), PR 101 (Synthetic Red Iron Oxide) – Daniel Smith Watercolour Paint
- Pbr 24 (Chrome Antimony Titanate) – Michael Harding Oil Paint
- PBr 24 (Chrome Antimony Titanate), Pbk 7 (Natural Brown Iron Oxide), PW 4 (Zinc White) – Golden QOR Watercolour Paint
- PW 6 (Titanium White), PBr 24 (Chrome Antimony Titanate) – Winsor & Newton Watercolour Paint
It’s worth noting that these pigment combinations make a great guide to mixing your own ‘Naples Yellow’.
3. The Same Pigment Can Have Different Names
There can be huge variations in colour names among manufacturers- even for the most commonly used colours. The blue pigment Copper Phthalocyanine was first sold under the trade name Monastral Blue, but is also known by many other names and spelling variations, including Monestial Blue, Helio Blue, Phthalo Blue, Thalo Blue, Winsor Blue, and Scheveningen Blue. The Colour Index International classifies Copper Phthalocyanine as simply Pigment Blue 15 (PB 15). Seeing this on the side of the paint tube, you can quite reliably predict that the paint is transparent, deep in masstone, and very strong in mixtures – traits that are typical in Phthalocyanine pigments.
4. You Can Identify Genuine Pigments
Genuine pigments are those which have some historical significance or particular characteristics, but are sometimes recreated using mixtures of other pigments. Viridian Green (PG 18), for example, was used by the Impressionists, but is sometimes recreated using Phthalocyanine Green pigment (PG 7). Another example is genuine Van Dyke Brown (PBr 8), a historical deep brown pigment made from iron oxide, clay, and bitumen, which is usually mimicked with a mixture of pigments. It’s important to note here that it’s easy to attach a certain romance to historical pigments, but they aren’t always the best. There are many toxic or non-lightfast pigments that have now been replaced with safer and more permanent modern pigments.
Top: Genuine Alizarin Crimson (non-lightfast pigment PR 83) mixed with Ultramarine Blue.
Bottom: Permanent Alizarin Crimson made with lightfast pigments PR 177, PV 19, and PR 149 in the same mixtures with Ultrmarine Blue.
5. The Pigment Colour Index Tells You How Many Pigments Are in the Paint
The number of pigments in a paint matters enormously to many artists. Single pigment colours – paints that contain only one pigment – are generally considered to be best in mixtures because the more different pigments are mixed together, the muddier the resulting colour. If single pigment colours are important to you, then the Pigment Colour Index is invaluable to make sure you are using a single-pigment version of a colour.
Why Do Different Colours Have the Same Colour Index Code?
All pigments vary in hue, chroma, and handling characteristics depending on the way they are manufactured and processed, but some entries in the Colour Index are more precise than others. Paints made using single pigment PY 3 (a pigment commonly known as Hansa Yellow Light), are almost always a bright, semi-transparent, lemon yellow. However, some Colour Index Codes cover a wide range of colours with very different characteristics. A good example of this is PBr 7 (Pigment Brown 7). It refers to a Natural Brown Iron Oxide, and due to the natural variations of iron oxides, paints labelled PBr 7 can vary from yellowish-brown to dull red. Pigment manufacturers can control these variations – Burnt Sienna is produced by heating Raw Sienna, which partially dehydrates the iron oxide, making it darker and redder. The same goes for Raw Umber and Burnt Umber, two other Brown Iron Oxide pigments. So, Raw Sienna, Burnt Sienna, Raw Umber, and Burnt Umber can be categorised under PBr 7, despite the fact that they are very different colours.
Left to Right: Burnt Umber, Raw Umber, Raw Sienna, and Burnt Sienna.
Artists instinctively build knowledge about the properties of colour as they are working. By familiarising yourself with the Pigment Colour Index you can identify exactly which pigments are best for your practice.
- White Pigments (Codes beginning PW)
- Yellow Pigments (codes beginning PY)
- Orange Pigments (Codes beginning PO)
- Red Pigments (Codes beginning PR)
- Violet Pigments (Codes beginning PV)
- Blue Pigments (Codes beginning PB)
- Green Pigments (Codes beginning PG)
- Brown Pigments (Code beginning PBr or NBr)
- Black Pigments (Code beginning PBk)
You can also read our Pigment Stories series to find out about the history behind some widely used pigments.
Good point: listing these pigment
combinations make a great guide to
mixing your own!
I find it very useful!
Eve:
I am getting back into watercolor
painting and try to learn as much as I
can about the paints Papers and
tools of the art. Thank you for your
articles. I feel the more I know the
better prepared I will be when mixing
and creating my works.
That’s so great to hear, thank you!
Love this article! It really is informative.
Do you happen to know which pigments
(by its color index) are toxic? I was
hoping to find such information online
but I’ve only managed to find generic
names like cadmium and cobalt which is
difficult to identify without the code in
paints with multiple pigments:)
Thanks Silvia! We will be publishing articles for each colour family, so you can look up individual pigments and you should find the information you’re looking for there. Toxicity is a complicated term to define and many pigments are potentially harmful to varying extents – usually when inhaled or ingested in dry powder form rather than in contact with the skin. But many artists choose not to use Cadmium and Cobalt pigments – Cadmium pigments are identified with the codes PR108, PY35, and PY37. And Cobalt pigments are PB28, PB35, PB36, PB72, PB73, PB74, PG19, PG26, and PG50. I hope that helps!
Handprint is a bit dated now but very
comprehensive:
https://www.handprint.com/HP/WCL/wate
rfs.html It looks in detail at colour-
fastness of watercolours.
Alas it misses ‘strontium yellow’ PY32
which I think is now only available in oils
What is pigment I don’t understand
please explain me what is pigment
colour I want to know
Is pigment is ready colour or need to mix
other things
Hi Arjun
Pigment is the coloured part of any paint. For instance, Ultramarine Blue is a pigment that at one time was made from Lapiz Lazuli rocks dug from the earth in Turkey. They ground those blue semi-precious gemstone rocks up and sold the powder to paint makers who mixed it with linseed oil to make blue oil paint. It was very expensive blue paint so was only used for the robe of the Madonna in Renaissance paintings. Many years later they found a way to heat certain metals and combine them with other chemicals and make a very similar blue in the laboratory. That blue powder was much cheaper. But you also mix it with linseed oil to make Ultramarine Blue oil paint, now that colour is much more affordable.
All paints are made from a coloured powder that is either finely ground rocks from the earth or created in a laboratory. It is a powder but it has no binder, nothing to glue it to the surface. It must be mixed with something else to make it into a paint. To make watercolour paint you mix the pigment with gum arabic. To make acrylic paint you mix the pigment with acrylic polymer. To make household paint you mix the pigment with a latex emulsion.
So pigment is not ready-made colour. You can buy it as a powder but it will need to be combined with a binder (oil, gum, emulsion, egg yolk, polymer, glue, etc) to turn it into a paint. If you add water to it and paint it on a surface, when the water dries the powder will all brush off and blow away. There are powdered paints that look similar to pigment, but they have a powdered glue in them that when wetted becomes a paint and will stick.
Not a lot of artists make their own paints. So most artists do not buy the pigments by themselves. Painters that use Egg Tempera paints do, though, because they make their paints fresh each day with dry pigments and egg yolk.
But, artists do want to know which pigments are in the paints they are buying. Because Winsor & Newton call their oil paint that is made with PB:15 Phthalocyanin Blue, Winsor Blue, and Schmincke Horadam watercolour using the same pigment calls it Sapphire, and Golden uses the same pigment in an acrylic paint they call Manganese Blue Hue – it helps to know that since the label says they all contain PB:15 then the painter knows that it is Phthalo Blue paint.
There aren’t that many pigments available to make paints. The reason there are many colours in some ranges of paints are because they mix some pigments together in different ways, so many paints are mixes of pigments. And knowing which pigments are in your tube, will help you predict how the colour will mix with other colours.
The pigment is the expensive part of any paint. That is why paints are priced in a series. The paints containing the more expensive pigments are priced higher than the paints containing less expensive pigments, even though they have the same binder in them.
I hope that is helpful.
This is such an amazing
explanation! Thank you so much
Julie.
Thank you, Maria! Glad you found it useful!
Super helpful. The point about just because it is the same code, it might not be the same colour is important. I have five tubes from different manufacturers (obviously got carried away) of PV53 diox purple and they are so different! And I use the codes as a guide for mixing my own colours – especially useful for Daniel Smith mixes eg Moonglow. Thanks
Great article, very informative.
Thank you, Frances
For those interested in a free and searchable
pigment database, check this out:
databasehttps://www.artiscreation.com/
The information you are giving us is SO
important and interesting. It must have
involved a lot of research. Thank you. I don’t
think it gives information about the
lightfastness of the different pigments but
maybe I’ve missed something?
You’re welcome Jennifer! I enjoyed writing it. I’ll be publishing resources for each of the pigment groups over the coming weeks, and I decided not to include lightfastness ratings for each pigment because it can vary depending on the medium and the way the paint is applied – but I will mention when a pigment has notable lightfastness concerns.
For my oil palette I use Michael Harding for
his use of single pigment colours. I find it
unnecessary to use Cobalt or Cadmiums
Thank you Evie, this is such an interesting,
informative and enjoyable read. I have a
fascination for colour and your article has
added much more detail for me, particularly
the fact that PBr 7 can look so different! I’m
really looking forward to the next one.
So glad you enjoyed it! Thanks Sue
In permanent crimson alizarin, PR177 was
recently scored as not lightfast, although
used in many paints as moonglow (Daniel
Smith), permanent red deep of Maimeri…
Apart this remark, great article
Ahh yes, I just looked into that and you’re right – thank you!
This is an incredibly well-written and well-
researched article. Ms. Hatch creates a
fantastic resource that should be required
reading for any art supply store employee.
Thank you Patrick, that’s very kind!
Evie, you’ve done it again.
! I love this research into pigments. It gives
me a deeper understanding and wonder
about what I am using. I also enjoyed your
piece on on black. Thanks so much.
Thank you Rita!
Thank you for this very clear and helpful
article. As a new ‘lockdown’ painter it is
exactly the information I’ve been trying to
find. I’m looking forward to the rest of the
series.
So glad you found it helpful Liz!
How to understand the logic of numbers, given to pigments? I mean – why, say, ultramarine is pb29 and cobalt is 28, and ceruleum is 35 / 36?
Hi Yasna, the numbers were assigned in the order in which the pigments were added to the colour index. Most pigments artists use today had already been developed so many appear at the beginning of the index. But you’ll notice that the most modern pigments (the quinacridones for example) have much higher numbers because they were added later!
Great post Evie, very thorough.
love these. Are Jackson’s planning to publish
them in hard copy? I would love a pigment
book.
Hi Kate
Nothing firm, but maybe in the future.
Good to see this made so easily available.
Thanks. Have owned and constantly use
Micheal Wilcox books on pigments and
paints and they changed my art skills sooo
much.