crystals-2308095

Characterization techniques The chemical compositions of both porcelains glaze and body were examined by portable energy-dispersive X-ray fluorescence spectrometer (EDXRF, OURSTEX 100FA, OURSTEX, Osaka, Japan). The EDXRF technology uses palladium (Pd) as excitation tube and works continuously in three different modes, effectively measuring the major elements (15 KV, 1 mA), trace elements (40 KV, 0.5 mA) and weight elements (40 KV, 1 mA), respectively. This spectrometer used a silicon driftdetector (SDD) with active area of 5mm2 equipped with one polymer window (MOXTEK AP 3.3 film). Combined with the introduction of a low-vacuum sample chamber, which can effectively reduce the absorption of characteristic spectra of light elements (like Na and Mg), such equipment had already been applied successfully in chemical composition analysis of ancient porcelains and ceramics [5-7].  The cross-sectional structure of three groups of glaze layers was studied by optical coherence tomography (OCT, HSL-2100, Santec, Aichi, Japan), which typically consisted of a swept light source with central wavelength around 1315-1340 nm, the imaging range was 0-20 mm and imaging depth was 3-3.5 mm. During testing in silicate materials with a 1.5 refractive index, the transverse and longitudinal spatial resolution was 2.4 μ m/pixel and 5.3 μ m/pixel, respectively. This technology has been successfully applied in the ancient Chinese ceramics and porcelains [8-10].  The morphology observation on both porcelain glaze and body was carried out by optical microscopy (OM, VHX-50000, Keyence, Osaka, Japan). The microstructure and elemental analyses of porcelain glaze and body (both surfaces and cross-sections) were conducted by scanning electron microscope (SEM) fixed with energy-dispersive X-ray spectrometer (EDS) operated in the back scattered electron image mode (TM3000, HITACHI, Tokyo, Japan). The confocal micro-Raman spectrometer (LRS, LabRAM XploRA, Horiba, Palaiseau, France) was performed on glaze surface to identify the phase constituents and a diode near-infrared (NIR) (532 nm) laser was applied for the excitation. The laser power was 300 mW, confocal pinhole diameter was 300 µm, slit width was 100 µm, grating groove per millimeter was 1800 T, spectral acquisition and imaging acquisition time was 20 s, and signal acquisition integration times were 2.