A combination of synchrotron techniques such as infrared micro-spectroscopy, micro X-ray fluorescence, micro X-ray absorption spectroscopy or micro X-ray diffraction was crucial for the outcome of the work. "On one hand, the paintings are arranged as superposition of multiple layers, which can be very thin. The micrometric beam provided by synchrotron sources was hence essential to analyze separately each of these layers. On the other hand, these paintings are made with inorganic pigments mixed in organic binders, so we needed different techniques to get the full picture" Marine Cotte, a research scientist at CNRS and an ESRF scientific collaborator explains.
The results showed a high diversity of pigments as well as binders and the scientists identified original ingredients and alteration compounds. Apart from oil-based paint layers, some of the layers were made of natural resins, proteins, gums, and, in some cases, a resinous, varnish-like layer. Protein-based material can indicate the use of hide glue or egg. Within the various pigments, the scientists found a high use of lead whites. These lead carbonates were often used, since Antiquity up to modern times, not only in paintings but also in cosmetics as face whiteners.
"This is the earliest clear example of oil paintings in the world, although drying oils were already used by ancient Romans and Egyptians, but only as medicines and cosmetics", explains Yoko Taniguchi, leader of the team.
Due to the large gap of time between the Bamiyan paintings and the Renaissance, it's unlikely that the knowledge of oil painting was transmitted from the East to Europe. It's more likely that it was independently discovered. As Taniguchi says, oil had been used with cosmetic pigments for thousands of years. For most of history, painters have not had access to mass produced or standardized formulas for paints. Each painter had to be an experimenter and chemist with his own secret recipes handed down by their various schools. If pigments mixed with oil were being used for one purpose (cosmetic) I'd expect that oil pigments for painting have been tried and forgotten several times over the millennia.
Hopefully, this will lead to more and better archaeology in Central Asia, one of the least studied parts of the Old World. When I taught a few classes in Ancient History, I was fascinated by the fact that most history concentrates on the outer edge of the Eurasian land mass and ignores the connecting region in the middle. We know that are was active. We know empires rose and fell there. But because of the difficulty of doing work there, the region has barely been studied, and most studies are as an extension of one of the periphery civilizations. There are wonderful things waiting to be found there, but they won't wait. Politics, thoughtless development, fundamentalist thugs, and climate change will destroy libraries worth of knowledge every year unless someone gets there first.