The Egyptians and Babylonians used lapis lazuli 6,000 years ago. In 1802, a French chemist synthesised cobalt blue. In 2009 scientists discovered YInMn Blue, otherwise known as Oregon Blue. But most of these pigments have limitations in terms of cost, stability, colour or toxicity. In 2020, researchers reported a new class of ‘cool’ blue colourants that are inexpensive, durable and more environmentally friendly.
For the last 200 years, cobalt blue has been a dominant commercial blue pigment because of its colour intensity, ease of synthesis and versatility. However, 33% of the colourant by mass is carcinogenic, making cobalt blue relatively expensive and environmentally harmful to produce. The Oregon State University researchers were inspired by the crystalline structure of a light-blue mineral called hibonite. The team systematically substituted aluminium ions in hibonite with cobalt, nickel or titanium ions. The resulting series of pigments showed a range of intense blue colours, some with reddish hues. The pigments were stable even when soaked in acidic or basic solutions. In contrast to cobalt blue, the new blues reflected near-infrared light, which could make them useful as ‘cool pigments’ in energy-saving, heat-reflecting coatings. Importantly, the cobalt concentration in the new compounds in hibonite blues was as low as 4% by mass, making the pigments cheaper and more environmentally friendly.
