What Pigment Numbers on Paint Tubes Mean for Artists

How are the standardized Color Index names and numbers assigned to pigments?

The Color Index International assigns these identifiers through a collaborative assessment process overseen by the Society of Dyers and Colourists and the American Association of Textile Chemists and Colorists.

• Chemical Structure: Each entry requires a distinct molecular composition that demonstrates a stable, repeatable performance profile.
• Coloristic Properties: The substance must undergo rigorous testing to document its specific hue, saturation, and lightfastness ratings.
• Manufacturing History: Applicants must provide evidence of commercial availability and industrial use to justify inclusion in the index.
• Standardization: The resulting alphanumeric code acts as a universal shorthand, replacing proprietary trade names with a verifiable technical identity that professionals rely on for archival consistency.

What is the difference between a single-pigment paint and a hue mixture?

Single-pigment paints rely on a solitary chemical agent for color, whereas hue mixtures combine multiple pigments to approximate a specific shade.

Prioritize single-pigment tubes when you need to maintain clean, chromatic intensity in complex glazing or layering techniques.

Why do some paint tubes list multiple pigment numbers on their labels?

Manufacturers often list multiple pigments to create a specific, complex color that would be difficult for an artist to replicate by hand. This is common in "convenience mixtures" like Payne’s Gray, which might combine PB29 (Ultramarine Blue), PBk7 (Carbon Black), and sometimes PR101 (Iron Oxide) to achieve a balanced, dark neutral. These tubes save time, but they can limit your control over the final temperature of a shadow or a tint.

One nuance involves the ratio of these pigments, which is rarely disclosed on the label. If a manufacturer changes the percentage of one pigment in a multi-pigment blend, the resulting color shift can be significant. This makes it difficult to achieve consistent results if you switch between brands, even if the label shows the same list of pigment codes.

How does the chemical composition of a pigment affect its lightfastness and permanence?

The chemical composition determines how a pigment’s molecular bonds resist degradation when exposed to ultraviolet radiation and atmospheric pollutants.

• Inorganic Pigments: These mineral-based compounds, such as iron oxides or cadmiums, generally offer superior resistance to fading over decades.
• Organic Pigments: Modern synthetic dyes, like quinacridones, provide intense brilliance but can vary wildly in their long-term stability.
• Molecular Stability: The specific crystalline structure dictates how effectively the pigment reflects light without breaking down into inert, colorless particles.
• Binder Interaction: The medium, whether oil or acrylic, acts as a protective shield that influences how quickly environmental factors reach the pigment.

What do the prefixes 'P', 'B', 'R', 'Y', and 'G' signify in a pigment code?

These prefixes denote the color category: P stands for Pigment, followed by B for Blue, R for Red, Y for Yellow, G for Green, V for Violet, Br for Brown, and Bk for Black. A lot of people assume these codes indicate the physical hue of the paint as it appears in the tube, but they actually describe the chemical classification. For instance, a tube labeled PBk7 is a black pigment, but it might appear as a warm, brownish-black rather than a cool, neutral black depending on its particle size.

How can artists use pigment numbers to predict how colors will mix on the palette?

Using pigment numbers allows you to predict mixing outcomes by identifying the dominant undertones of your colors. If you mix two colors that share a common pigment, the resulting blend remains clean and vibrant. For example, mixing a yellow that contains PY3 with a green that contains PG7 and PY3 will yield a predictable, harmonious result because the shared PY3 acts as a bridge between the two colors.

One exception occurs when you mix pigments with vastly different particle sizes or oil absorption rates. Even if the chemistry seems compatible, the physical properties of the pigments can cause the mixture to separate or turn "muddy" on the palette. Always check the pigment codes to make sure you aren't fighting against clashing undertones, but be aware that the physical behavior of the paint in the binder also influences the final result.

Why might the same pigment number produce slightly different shades across different paint brands?

Yes, variations occur because brands use different binders, additives, and grinding levels. A pigment with a 5-micron particle size will appear more transparent and vibrant than the same pigment ground to 20 microns, significantly altering the tinting strength and handling characteristics of the final paint film.

What is the significance of the 'PW' designation for white pigments in professional paints?

The PW designation identifies inorganic white pigments, which are essential for adjusting the opacity and value of other colors in a painting.

Use these codes to select the appropriate white for your technique, such as choosing the more transparent PW4 for delicate glazing or the highly opaque PW6 for solid highlights.