Craftsmen in ancient China were using complex machines to work jewellery long before such devices are traditionally thought to have been invented.
The grooves seem to have been machine-worked by a complex device
Dr Peter Lu claims spiral grooves on 2,550-year-old jade rings must have been made by a precision "compound" machine.
As the name suggests, compound machines comprise two or more machines with different motion that have been linked together to perform precision work.
Dr Lu, of Harvard University, US, has published his research in Science.
Previously, the earliest known historical references to compound machines come from writings attributed to Hero of Alexandria that are dated to the First Century AD.
Carved decorations on jades from ancient China are generally thought to have been made by hand, or with simple machines that worked with a single movement.
OLDEST COMPOUND MACHINE
Consisted of two or more machines working together
Contained a stylus suspended over a rotating turntable
Mechanism created spaced grooves on a jade ring
The ornamental jade burial rings reported in Science come from the so-called Spring and Autumn period (771 to 475 BC) and have been excavated from hoards and from tombs belonging to ancient officials and nobles.
The machine that carved the grooves would have linked rotational and linear motion, perhaps using a stylus suspended over a rotating turntable, says Dr Lu.
"The complex machine that created these spiral grooves may also be among the ancestors of the crank in China... sculptures to have mechanised a variety of agricultural processes such as milling and winnowing," Dr Lu writes in Science magazine.