Nanostructure and phase imaging of ancient ceramics using full field hard x-ray microscopy

What started as a philosophical concept more than 2400 years ago by introducing átomos, the indivisible, still puzzles scientists because state and order of atoms determine the properties of all materials. It remains a mystery whether the potters in ancient Greece were aware of this concept when they created their famous black and red vessels. But it is obvious that they possessed the knowledge to change macroscopic properties of the material by controlling processes which happen at the nano-scale. In this presentation I will present the application of full field hard x-ray transmission microscopy (TXM) to the analysis of Roman ceramics (Terra Sigilatta). The x-ray microscope on BL 6-2 at the Stanford Synchrotron Radiation Lightsource is capable of imaging in the energy range from 5-14 keV, with up to 30 nm resolution [1]. Recent advances in data collection and evaluation [2] paved the way for single pixel x-ray absorption near edge structure (XANES) spectroscopy, combining the high resolution and large field of view of full-field transmission X-ray microscopy with the chemical information derived from X-ray absorption spectroscopy in order to trace chemical phase transformations in 2D and even 3D [3]. Aim of this study is to gain knowledge about the firing protocols used for production of the ceramics. This is crucial for a better understanding of the manufacturing process of Terra Sigillata and the development of the iron oxide-rich clay material based ceramic technology in the Mediterranean: from the remarkable proto-geometric vases to classical Attica black-gloss figurines and finally to the high-gloss terra sigilatta - all obtained through control of vitrification and redox chemistry. Results from the TXM study and complementary analyses using micro-X-ray fluorescence [4] and time of flight secondary ion mass spectroscopy (TOF-SIMS) support the hypothesis of a three step firing process showing that the potters were able to control/change the nano-porosity of the material in the first two steps, consequently providing control over oxygen diffusion, and therefore the color of the material, in the third step