Editor's Note: Every week we look at a work of art or a cultural relic that puts the spotlight on China's heritage.

A five-month exhibition titled Zhejiang Green Proto-Porcelain and Excavation Achievement of Deqing Kiln Sites recently wowed art enthusiasts and experts at Yanxi Hall of the Palace Museum, demonstrating the mysterious charm of this ancestor of Chinese porcelain.

The green proto-porcelain specifically refers to high-temperature fired green-glazed kiln ware made from the Shang Dynasty (c.16th century-11th century BC) to the Western Han Dynasty (206 BC-AD 24).

To picture an accurate timeline of green proto-porcelain's development, a field team comprised of researchers from the Palace Museum, the Zhejiang Archaeology Institute and Deqing Museum conducted an excavation from March to May 2007 at Huoshaoshan kiln site, in Deqing county, Zhejiang province.

The Zhejiang Archaeology Institute then continued to excavate in the area kiln sites such as Nanshan, Tingziqiao and Dayuanping. A large number of green proto-porcelain wares were unearthed from these excavations, which have provided solid evidence for studies of green proto-porcelain's development, and transformation from proto-porcelain to real porcelain.

"Green proto-porcelain ware was used by all walks of life in old times," Chen Lihua, vice-curator of the Palace Museum, says.

The 105 exhibited objects, which are from the collections of the Palace Museum, Deqing Museum and Shaoxing Museum, and include unearthed specimens from northern Zhejiang province, cover a wide variety of ritual objects, weapons and farming tools.

The number of proto-porcelain kiln sites in Zhejiang is more than 100, and they have produced variously shaped wares.

The most worthy of mention are wares for ritual use found from the late Western Zhou Dynasty (c. 11th century-771 BC) to early Spring and Autumn Period (770-476 BC). They were modeled on bronze vessels, such as you, ding and gui. Complicated designs are frequently seen on the exteriors of the vessels. Carved patterns are usually large, rough and randomly arranged.

A cylindrical you vessel that was unearthed from the Huangfendui grave is one of the finest examples produced in the Western Zhou Dynasty.

"Ritual vessels symbolize wealth and status. Their appearance indicates the development of social hierarchy," says Geng Baochang, chairman of the China Ancient Pottery and Porcelain Institute and researcher at the Palace Museum.

After the middle Spring and Autumn Period, ritual proto-porcelain wares vanished. Those for practical use, such as bowls, became dominant. At the same time, decorative patterns also became less prevalent. Only patterns of symmetrical arcs and water waves survived the transition.

Peking University professor Li Boqian points out that questions like when and where the proto-porcelain first appeared and why the wares used for rituals suddenly disappeared are still debatable. But future finds should point the way forward.