Ancient pollen could lead scientists to the kilns where the figures in China's terracotta army were made.
The army was designed to guard the tomb of China's first emperor
The 2,200-year-old clay army of 8,000 soldiers, 300 horses and 200 chariots guards the tomb of Qin Shihuang, the first emperor of China.
Soils from different regions contain distinct pollen "signatures", reflecting variations in vegetation.
This could help solve the mystery of where the clay figures were made, says the Journal of Archaeological Science.
Hu Ya-Qin from the Chinese Academy of Sciences in Beijing and colleagues crushed fragments of terracotta from a horse and a soldier, digested the ground-up bits of clay with acid and spun the mix to separate out the different components.
The team looked at the resulting residues under a microscope and identified 32 types of pollen.
They found the horse and soldier had different pollen signatures.
Pollen from the terracotta horse came mainly from trees; a similar pollen signature is found in soil taken from pits in the emperor's mausoleum.
Pollen from the terracotta warrior came mainly from herbaceous plants.
The researchers argue that the horses were made near the mausoleum. Dr Hu told Chemistry World magazine that this made a lot of sense.
The soldiers do not seem to have been made locally
The horses were heavier than the soldiers, with more fragile legs. Making them locally would have minimised the effort involved in transporting them and reduced breakages, he explained.
Several ancient kilns have previously been found in this region of China, but it has been difficult to determine whether any were used to make the terracotta army. The research may help scientists trace an origin for the clay figures.
Dr Arlene Rosen, from the Institute of Archaeology at University College London, UK, said the research was "one important step towards solving the mystery of where the clay army came from".
But she added: "Using pollen has its advantages and disadvantages."
For example, if the clay came from an area near a river or stream, it could contain pollen from many sources washed in by the water. And if the clay was from a very old source, it could preserve information about vegetation that existed long before the time of the terracotta army.
Dr Rosen said there were more accurate ways to trace the source of clay used in archaeological artefacts. These include analysis of the temper - coarse-grained material added to stop the clay from cracking as it dries - through X-ray diffraction.