How new colors are invented: the chemistry behind pigment discovery

Every so often a headline announces that scientists have "invented a new color." Strictly speaking, they haven't. The human eye can perceive millions of shades, and chemistry can't add a hue to the visible spectrum. What chemists can do is discover new pigments: new materials that produce a color more brightly, more durably, more safely or more cheaply than anything before them.

For the paint and coatings industry, that distinction matters. A new pigment can open up colors that were previously impractical outdoors, replace a toxic ingredient, or add performance such as heat reflection. This article explains how pigments create color, how new ones are found, and what it takes to get one from a lab bench into a can of paint.

How pigments create color

Color is what's left after a material interacts with light. A pigment looks blue because it absorbs other wavelengths and scatters blue light back toward your eye. What decides which wavelengths are absorbed is the material's electronic structure, and there are a few main ways that happens:

• Transition metal ions. In many inorganic pigments, metal ions such as cobalt, chromium or manganese sit inside a crystal lattice. The arrangement of the surrounding atoms determines which energies of light those ions absorb. Change the arrangement, and you change the color.
• Charge transfer. Some pigments absorb light when an electron jumps from one atom to another. Many iron oxide yellows, reds and browns get their color this way.
• Band gaps. Semiconductor pigments, such as the cadmium yellows and reds, absorb all light above a certain energy. The size of the gap sets where the cut-off falls, which is why these pigments produce such clean, saturated colors.
• Conjugated organic molecules. Organic pigments like phthalocyanines and azo pigments contain long chains or rings of alternating bonds that absorb specific wavelengths. Small changes to the molecule can shift the shade.
• Structural color. Effect pigments create color through interference rather than absorption. Thin layers of metal oxide on mica or glass flakes reflect certain wavelengths more strongly, producing pearlescent and color-shifting finishes.

A useful distinction for coatings: a pigment is an insoluble particle dispersed in a binder, while a dye dissolves in the medium. Paints rely mostly on pigments because they offer opacity and durability.

A short history of pigment discovery

Many important pigments were found by accident, and nearly all of them took years to become practical.

• Prussian blue was discovered by chance in Berlin in the early 1700s, and became one of the first modern synthetic pigments.
• Synthetic ultramarine arrived in the 1820s, after a prize was offered in France for a way to make the color without grinding up costly lapis lazuli.
• Titanium dioxide was commercialized as a white pigment in the early twentieth century and gradually replaced lead white. Today it is the most widely used pigment in paint by far.
• Phthalocyanine blues and greens, introduced in the 1930s, gave formulators intense, highly durable organic colors.
• Diketopyrrolopyrrole (DPP) reds, developed in the 1980s, made bright, weather-resistant reds practical for demanding uses like automotive finishes.

The pattern repeats: a discovery, followed by a long period of learning how to make the material consistently, how to disperse it, and whether it survives sunlight, heat and chemicals.

Case study: an accidental blue

One of the best-known recent examples is YInMn Blue, named for its components: yttrium, indium and manganese. In 2009, a research group at Oregon State University was studying new materials for electronics. When they heated a mixture of these oxides at high temperature, one sample came out of the furnace a vivid blue.

The color comes from manganese ions held in an unusual geometry within the crystal, which changes how they absorb light. Beyond its striking shade, the pigment turned out to be very stable and to reflect a large share of near-infrared radiation, a useful property for "cool" coatings that keep roofs and buildings from heating up in the sun.

YInMn Blue also illustrates how long the path to market is. It took years of scale-up, testing and regulatory review before the pigment was approved for commercial use in coatings and plastics, and its high cost, driven partly by indium, still limits where it is used.

What makes a pigment commercially viable

Discovering a beautiful color is only the start. For paint and coatings, a pigment has to clear a long list of hurdles:

From lab discovery to a can of paint

Bringing a new pigment into commercial coatings typically follows several stages, each with its own experiments and decisions:

1. Synthesis and characterization. Confirm the structure, understand what controls the color, and identify variations that improve it.
2. Scale-up. Move from grams to tonnes while controlling particle size, crystal form and purity, all of which affect color.
3. Surface treatment. Many pigments are coated to improve dispersion, durability or compatibility with specific binders.
4. Formulation testing. Evaluate the pigment in waterborne, solventborne and powder systems, at different loadings and in combination with other pigments.
5. Performance and durability testing. Run accelerated weathering, outdoor exposure, heat and chemical resistance tests.
6. Regulatory registration. Complete safety assessments and register the substance in each market where it will be sold.
7. Color matching and customer approval. Coatings makers then build the new pigment into their own color systems and customer-specific matches.

Even after a pigment is commercially available, every coatings company that adopts it runs its own series of formulation and test requests. Those requests involve sales, the lab, technical service and often regulatory teams, which is exactly the kind of multi-step, multi-person work that's easy to lose track of without software designed for coatings development.

Where pigment innovation is heading

• Infrared-reflective pigments that let darker colors stay cooler in the sun, cutting energy use in buildings and vehicles.
• Replacements for heavy-metal pigments, as regulations continue to tighten around lead, chromium and cadmium compounds.
• More advanced effect pigments that deliver depth, sparkle and color travel, especially for automotive and consumer goods.
• Lower-carbon and bio-based colorants as manufacturers look at the environmental footprint of every raw material.
• Computational discovery, where modeling and machine learning help predict promising structures before anything goes into a furnace.

Frequently asked questions

Can scientists invent a completely new color?

Not in the sense of a hue the human eye has never seen. What chemists invent are new pigments: new materials that produce a color with better brightness, durability, safety or performance than what was available before.

What is the difference between a pigment and a dye?

A pigment is an insoluble particle that is dispersed in a binder, such as the resin in paint. A dye dissolves in the medium it colors. Paints and coatings mostly rely on pigments because they are generally more durable and opaque.

How long does it take to bring a new pigment to market?

Typically many years. After discovery, a pigment has to be scaled up, tested for durability and compatibility in different binder systems, assessed for safety and registered with regulators before it can be sold for commercial coatings.

Interested in other advances in coatings chemistry? Read our guide to self-healing coatings.

Sources and further reading

• Smith, A. E., Mizoguchi, H., Delaney, K. et al. (2009). "Mn³⁺ in Trigonal Bipyramidal Coordination: A New Blue Chromophore." Journal of the American Chemical Society
• U.S. EPA: Summary of the Toxic Substances Control Act (TSCA)
• European Commission: REACH Regulation overview