Every serious watercolour paint carries a small code on its label - something like PB29 or PV19. That code is the Colour Index, and it is the most useful piece of information on the tube. It tells you exactly which pigment is in the paint, which in turn tells you how it will mix, granulate, stain and age. This guide explains how to read it.
What is the Colour Index?
The Colour Index International (CII) is a worldwide reference that assigns a generic name to every pigment and dye by colour and chemistry. A watercolour labelled "Ultramarine Blue" might be made by anyone; a watercolour labelled PB29 is the pigment ultramarine, no matter who made the paint.
The code letters explained
- PB - Pigment Blue (e.g. PB29 Ultramarine, PB15 Phthalocyanine Blue, PB35 Cerulean)
- PR - Pigment Red (e.g. PR254 Pyrrole Red, PR108 Cadmium Red)
- PV - Pigment Violet (e.g. PV19 Quinacridone, PV23 Dioxazine)
- PY - Pigment Yellow (e.g. PY150 New Gamboge, PY53 Chrome Titanate)
- PG - Pigment Green (e.g. PG18 Viridian, PG7 Phthalo Green)
- PBr - Pigment Brown (e.g. PBr7 Burnt Sienna)
- PBk - Pigment Black, PW - Pigment White, PO - Pigment Orange
Why single pigments matter
A colour made from one pigment mixes cleanly because only one chemistry is interacting on the paper. It also shows its transparency and granulation honestly. A "convenience" colour blended from three pigments can look beautiful straight from the tube but muddies fast in mixes and hides what each component is doing. When you know the code, you can predict the behaviour.
Using the Colour Index when you buy
Match the code to your need: a granulating sky blue wants PB35 (Cerulean) or PB29 (Ultramarine); a staining, intense blue wants PB15 (Phthalo); a transparent, permanent rose wants PV19 (Quinacridone). If the code is missing from a label, you cannot verify what is in the pan or how it will age. Browse our pigment encyclopaedia by Colour Index code, use the Colour Index Finder to match a pigment across our range, and read the full watercolour range with every code published.