Rare Iron Oxide Found in Ancient Chinese Tea Bowls

At the top, a modern replica of a Tenmoku tea bowl with "oil spot" surface patterns. At the bottom, a close-up of the oil spot pattern from an ancient Jian ware provided by the museum of Jian province.

(Image credit: Weidong Li and Zhi Liu)

Ancient Chinese tea bowls might hold the recipe for a rare form of iron oxide that scientists have had a hard time making in the lab.

Pure epsilon-phase iron oxide was unexpectedly discovered in the glaze of silvery Jian bowls made 1,000 years ago, a group of researchers announced this week.

Jian ceramic wares were created in China's Fujian Province during the Song dynasty between A.D. 960 and 1279. Today, examples can be found in museums like the Smithsonian's Freer and Sackler galleries in Washington, D.C., and the Metropolitan Museum of Art in New York. But Jian bowls even had international appeal back in their day: They were highly valued in Japan, where they were used in tea ceremonies and known as Yohen Tenmoku. [Images: Ancient Mural Tomb Discovered in China]

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Beyond retaining heat (an important quality for tea-drinkers), Jian vessels were famous for their dark, lustrous glaze, which was often streaked with patterns likened to "hare's fur," "oil spots" and "partridge spots." These characteristic designs came from molten iron flux in the glaze, which flowed down the sides of the bowls and crystallized into iron oxides while cooling in the kiln, researchers say.

A team of scientists, led by Catherine Dejoie of Lawrence Berkeley National Lab in California, wanted to investigate the microstructure and local chemical composition of this type of ancient pottery. They used X-ray diffraction and electron microscopy techniques to analyze the tiny quirks on Jian pottery fragments provided by the museum of the Fujian province. Hare's fur patterns on Jian bowls, once thought to contain just the mineral hematite, were found to have small quantities of epsilon-phase iron oxide, the scientists said. The researchers also found that oil spot patterns, thought to be made of the mineral magnetite, remarkably contain large quantities of pure epsilon-phase iron oxide.

Megan has been writing for Live Science and Space.com since 2012. Her interests range from archaeology to space exploration, and she has a bachelor's degree in English and art history from New York University. Megan spent two years as a reporter on the national desk at NewsCore. She has watched dinosaur auctions, witnessed rocket launches, licked ancient pottery sherds in Cyprus and flown in zero gravity. Follow her on Twitter and Google+.