*2.3. XRD*

XRD was used to characterize the surface of the light and dark regions; the edge of a slice and a powder sample of the Dzi bead were investigated to determine its structure. Powder XRD was conducted with a Rigaku Ru200BVH diffractometer equipped with a Co K<sup>α</sup> (λ = 1.8 Å) X-ray source. The diffraction patterns were measured over a 2θ range of 2◦ to 82◦ . The diffraction patterns of quartz (SiO2), graphite and copper oxide, CuO, were used as references to compare with the crystal structure of the Dzi bead. The reason for a graphite and copper oxide reference will become clear in the discussion below. XRD of the Dzi bead surface and the edge of a slice was conducted using the VESPERS (Very Sensitive Elemental and Structural Probe Employing Radiation from a Synchrotron) beamline of the Canadian Light Source [14]. It is a hard X-ray beamline equipped with optical elements to deliver a polychromatic beam (pink beam) and multibandpass monochromatic beams (using a double-multilayer and double-crystal monochromator with Si(111) crystals, respectively) as well as microbeam (using a Kirkpatric-Baez (KB) mirror) capabilities for XRD, XRF and imaging [14,15]. Using VESPERS (Very Sensitive Elemental and Structural Probe Employing Radiation from a Synchrotron), XRD was performed with monochromatic X-rays at 8 keV (1.55 Å)~Cu K<sup>α</sup> and 12 keV (λ = 1.03 Å), and the diffracted beam was detected by a Pilatus 1M pixel area detector. The diffraction rings were converted to intensity versus 2θ plots for easy comparison with the references. It should be noted that monochromatic X-rays from the synchrotron are tunable in energy, of a higher energy resolution and at least 10<sup>4</sup> times brighter than those of laboratory sources, making the technique more desirable for faster acquisition and higher-quality data for Rietveld refinement, and the microbeam (~5 µm) allows for small area diffraction and imaging.
