Scientists crack mystery of ancient Chinese pottery found in shipwreck
X-ray fluorescence reveals exact origin of porcelain recovered from the ocean floor. Andrew Masterson reports.
Researchers have succeeded in pinpointing the exact origins of 700-year-old Chinese pottery items recovered from a shipwreck.
In a paper published in the Journal of Archaeological Science, scientists from the University of Illinois and The Field Museum, both in Chicago, US, report the pioneering use of a technique called portable x-ray fluorescence (pXRF) to pinpoint the exact kiln complexes in China in which the artefacts were fired.
The pottery – items made from a bluish-white porcelain known as qinbai – are held as a collection at the Field Museum. They were first found in the late 1980s on board a shipwreck discovered by fishermen operating in waters between the Indonesian islands of Java and Sumatra.
The haul was later carefully salvaged and acquired by the museum. Initial dating placed the wreck in the mid-to-late Thirteenth Century, but more recent work has pushed that estimate back another century.
Most likely on a journey from Quanzhou in south eastern China to the Javanese port of Tuban, the ship sank, taking an estimated 100,000 ceramic vessels and 200 tons of iron to the ocean floor.
Qinbai ware was produced between 960 and 1368 CE. There was a major production centre at Jingdezhen in Jiangxi province, but it was also made, at varying degrees of quality, in several other places. Archaeological surveys have uncovered a multitude of kiln complexes.
Based on visual inspection, ceramics experts hypothesised that the museum’s collection originated from kilns at Jingdezhen, Dehua, Huajiashan and Minqing, but were unable to formally exclude other possibilities.
Wenpeng Xua, Lisa Nizioleka, Gary M. Feinman decided to see if pXRF could settle the matter.
X-ray fluorescence involves directing an x-ray beam at a target. The energy of the beam is high enough to displace electrons in the inner shells of the atoms contained within the target.
The displacement occurs because of the difference between the energy of the beam and the energy holding the electrons in orbit. When an electron is knocked out of orbit, the affected atom will immediately recruit another from the next fixed orbit further away and move it to fill the gap. In the process, the electron sheds energy, allowing a measurement that conclusively identifies the element.
With the process thus able to provide a comprehensive suite of the elements present, and their relative densities, the researchers set about analysing the glazes and pastes on 129 pieces of qinbai. The mix of elements, they reasoned, should be in part geographically determined, so should correlate with those found in each of the kiln complexes.
These had earlier been measured using pottery shards recovered from each site.
The scientists originally measured 44 elements, but eventually narrowed the selection to just 13, including magnesium, phosphorus, lead, silver and cadmium.
Comparing the results to the control data obtained from the kiln complexes, the results showed that the initial visual inspections had been correct.
“Comparative analysis of glaze and paste compositions … finds that glaze compositions are sufficient to distinguish between products from different kiln complexes,” the scientists report.
The pXRF fine detail, however, also opens up new avenues for investigating the different inputs and techniques used to create qinbai, fleshing out understanding of twelfth century manufacturing in China.