Materials Scientists Develop Durable, Vivid and Non-Toxic Pigments
A new series of inorganic pigments in vivid shades of red, yellow and orange have been made by modifying the structure of a rare Norwegian mineral.
A team of researchers at Oregon State University (OSU) has developed a series of inorganic pigments in vivid shades of yellow, orange and red by modifying the structure of thortveitite, a rare silicate mineral first discovered in Norway.
These new materials combine high color stability, low toxicity and potential energy-saving properties for use in surface coatings.
Published in Chemistry of Materials, the study was led by Mas Subramanian, professor of chemistry at OSU, who is well-known for the discovery of YInMn Blue – the first inorganic blue pigment discovered in two centuries since the discovery of Cobalt Blue in 1802. The latest pigments are derived from a structural analogue of thortveitite, which naturally includes the elements scandium and yttrium.
Creating color through crystal structure
While thortveitite itself is not known for producing intense color, the researchers were able to manipulate its crystal lattice by substituting nickel, zinc and vanadium. This combination yielded pigments in a range of saturated yellow, orange and red tones.
“The resulting color depends on the concentration and structural environment of divalent nickel, which is the primary chromophore responsible for the color,” said Subramanian, University Distinguished Professor of Chemistry and the Milton Harris Professor of Materials Science in the OSU College of Science.
Chromophore
A chromophore is a molecule (or section of a larger compound) that absorbs and reflects specific electromagnetic radiation, creating its color. In inorganic compounds, this is often due to the presence of transition metal ions.
Divalent nickel
Divalent nickel refers to nickel ions that have a +2 charge (Ni²⁺). This oxidation state affects how the ion interacts with light and can influence the color of the compound it is part of.
Nickel is already known for generating yellow and green hues in inorganic chemistry, but its role in producing orange and red tones is less common. By carefully adjusting the concentration and local structural environment of nickel ions, the team successfully extended the color range achievable with this element.
Thermal and chemical resilience
The pigments were synthesized at relatively low temperatures – around 750 °C –and are able to retain their color and structure after exposure to high temperatures and acidic conditions. This thermal and chemical stability makes them viable candidates for industrial-scale manufacturing and application in coatings that demand durability.
In addition to being colorfast, the new pigments also carry energy-saving potential; their ability to reflect heat from the sun means that buildings and vehicles coated in them will require less air conditioning. This characteristic could make them particularly useful for reducing energy use in warm climates.
Rational pigment design
The search for inorganic pigments that are both vibrant and safe has long been constrained by stability and toxicity concerns.
“Because of that, currently used inorganic yellow, orange and red pigments are being phased out for use in large-scale coatings and color applications,” Subramanian said. “A few replacements have been suggested but they all have stability issues and most are not commercially viable.”
“Most pigments are discovered by chance,” Subramanian continued. “The reason is because the origin of the color of a material depends not only on the chemical composition, but also on the intricate arrangement of atoms in the crystal structure. So, someone must make the material first in a laboratory, then study its crystal structure thoroughly to explain the color.”
Subramanian’s group aims to shift the pigment discovery process from one based on serendipity to one informed by crystal chemistry and computational modeling. However, predicting a crystal structure that will produce an inorganic pigment of an intense, desired color is still a challenge.
“Serendipity will still play a role in new pigment discoveries as science doesn’t always follow a prescribed path, and that adds to the excitement of doing color research,” Subramanian said. “But our approach holds the promise of accelerating the development of new pigments with targeted colors and functionalities. More and more, we’re gaining an understanding of the complex interplay between chemical composition, crystal structure and light interaction to precisely control the absorption and reflection of light across the visible spectrum.”
Reference: Lin YC, Verma A, Li J, Ramirez AP, Subramanian MA. Intense yellow/orange/red pigments based on a Thortveitite-like structure without toxic elements: Zn2–xNixV2O7. Chem Mater. 2025;37(13):4665-4673. doi: 10.1021/acs.chemmater.5c00324
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