The researchers relied on a combination of synchrotron techniques, including infrared micro-spectroscopy, micro X-ray fluorescence, micro X-ray absorption spectroscopy and micro X-ray diffraction.
"On one hand, the paintings are arranged as superposition of multiple layers, which can be very thin," said Marine Cotte, a research scientist at CNRS and an ESRF scientific collaborator.
Taniguchi’s collaborators used X-ray beams produced by the European Synchrotron Radiation Facility in Grenoble, France, to determine the composition and crystal structures of pigment particles in the colours.
The synchrotron facility produces extremely bright X-ray beams, which are essential for getting enough data from such small samples.
The Bamiyan caves sit behind the gigantic statues of Buddha that were destroyed by the Taliban in 2001.
Bamyan lies on the Silk Road which lies in the Hindu Kush mountain region, in the Bamiyan Valley.It is believed that the upper parts of their faces were made from great wooden masks or casts.The rows of holes that can be seen in photographs were spaces that held wooden pegs which served to stabilize the outer stucco.The Bamiyan caves are now a designated UNESCO World Heritage site.The researchers removed tiny samples of the painted surface (typically less than 1 millimetre across) for analysis using state-of-the-art techniques.