Ancient Chinese tea bowls might hold the recipe for an extremely rare iron compound that scientists are finding very difficult to create using modern techniques in the lab.
New analysis of ancient Jian wares reveals the distinctive pottery contains an unexpected and highly unusual form of iron oxide.
This rare compound, called epsilon-phase iron oxide, was only recently discovered and characterised by scientists and so far its has been extremely difficult to create with modern techniques.
"What is amazing is that the 'perfect synthesis conditions' for epsilon-phase iron oxide were encountered 1000 years ago by Chinese potters," said Catherine Dejoie, scientist at Berkley Lab's Advanced Light Source and ETH Zurich.
The study by an international team of researchers from China, France, Switzerland and US, could lead to an easier, more reliable synthesis of epsilon-phase iron oxide, enabling better, cheaper magnetic materials including those used for data storage, researchers said.
Jian wares, such as tea bowls, are famous for their shiny black glaze and variable brown and silvery surface patterns known as "oil spot" and "hare's fur."
The ceramic bowls, produced thousands at a time in giant kilns, were made during the Song dynasty in the Fujian Province of Southeast China between 960 and 1279 AD. Today, surviving Jian bowls are highly prised.
To make the pottery, ancient artisans used local iron-rich clay coated with a mixture of clay, limestone, and wooden ash.
Kiln temperatures of 1300 degrees Celsius hardened the clay, melted the coating, and bubbled oxygen within the glaze, pushing iron ions to the surface.
As the glaze cooled, molten iron flux flowed down the sides of the ceramics and crystallised into iron oxides imparting characteristic patterns.
The new analysis shows hare's fur patterns contain small quantities of epsilon-phase iron oxide mixed with hematite, while oil spot patterns boast large quantities of highly pure epsilon-phase iron oxide.
Epsilon-phase iron oxide was first identified in 1934, and only within the last ten years has it been fully characterised.
Marked by extremely persistent magnetisation, epsilon-phase iron oxide could hold the key to better, cheaper permanent magnets used in data-storage and other electronics.
Moreover, the epsilon phase is non-toxic and highly resistant to corrosion. Unfortunately, modern synthesis techniques have only managed to grow tiny, crystals often contaminated with hematite.
The study was published in the journal Scientific Reports.
