Ultramarine Blue Pigment vs Phthalocyanine Blue: Detailed 2025 Comparison

Choosing the right blue pigment is a critical formulation decision. Two of the most widely used blue pigments are ultramarine blue (Pigment Blue 29) and phthalocyanine blue (Pigment Blue 15, PB15). While both are trusted blue colourants, they differ significantly in shade, heat stability, acid resistance, and application suitability. This detailed comparison helps formulators at SKU Pigments customers make the right selection.

Shade and Colour Character

Ultramarine blue (PB29) exhibits a warm, reddish-blue shade — often described as a classic sky blue or cobalt-like tone. Phthalocyanine blue (PB15) delivers a greenish-blue, cooler shade with significantly higher tinting strength per unit weight.

For applications requiring a warm, clean blue — such as cosmetics, architectural paints, and certain plastics — ultramarine blue is the preferred choice. For deep, vivid greener blues in printing inks and industrial coatings, PB15 may be preferred.

Heat Stability

Ultramarine blue heat stability is a standout advantage. PB29 is stable up to 400°C, whereas PB15 begins to show shade shifts at approximately 200°C in some polymer systems. For high-temperature plastics processing above 200°C, ultramarine blue is the safer choice.

In polypropylene injection moulding at 230°C+, ultramarine blue maintains shade consistency. Phthalocyanine blue can also cause warpage in crystalline polymers like PP, a well-documented processing issue.

Acid Resistance

A key limitation of ultramarine blue is its sensitivity to acid. In strongly acidic environments (pH below 3), the alumino-silicate framework can be attacked, causing colour loss. Phthalocyanine blue, as an organic pigment, is unaffected by acid.

This means phthalocyanine blue is preferred for acidic formulations or environments where ultramarine blue would be unstable.

Toxicity and Regulatory Profile

Ultramarine blue is FDA-approved for cosmetics, including eye area products, and is listed in EU Cosmetics Regulation Annex IV. Phthalocyanine blue is generally considered safe but lacks approval for the same cosmetic applications in many jurisdictions.

For skin-contact and cosmetic applications, ultramarine blue is the clearly preferred and regulatory-compliant option.

Cost Comparison

Ultramarine blue is generally less expensive per kilogram than phthalocyanine blue. However, because PB15 has significantly higher tinting strength, the effective cost per unit of colour can be lower for PB15 in some applications.

For cost-conscious formulators where either pigment is technically acceptable, ultramarine blue from SKU Pigments offers an excellent balance of performance and economy.

Summary: Which Blue Pigment Should You Choose?

Choose ultramarine blue when: you need cosmetic approval, high heat stability in plastics, a warm reddish-blue shade, or compliance with sensitive regulatory requirements. Choose phthalocyanine blue when: you need very high tinting strength, a greenish-blue shade, acid-resistant formulations, or lower cost per unit of colour in specific systems.

Contact SKU Pigments for technical guidance and samples to help you determine the best pigment for your specific application.

Frequently Asked Questions

Is ultramarine blue stronger than phthalocyanine blue?

Phthalocyanine blue (PB15) has significantly higher tinting strength per gram than ultramarine blue. However, ultramarine blue has superior heat stability and regulatory approval for cosmetics.

Can I use ultramarine blue and phthalocyanine blue together?

Yes, blending PB29 and PB15 is common in paint formulations to achieve custom blue shades combining the warmth of ultramarine with the tinting strength of phthalocyanine blue.