Nondestructive study of glassy matrix of celadons prepared in different firing temperatures

Firing temperature is an essential indicator for the level of the manufacturing technology of ancient ceramics. Current techniques for measuring the firing temperature of ceramics are generally destructive and very complex. In this work, a series of celadon fragments were prepared at different firing temperatures (from 900 to 1,300 degrees C) and studied by Raman spectroscopy, X-ray fluorescence (XRF), and X-ray diffraction (XRD). The XRD results show that raw materials were dissolved and melted completely to form the glass matrix of a glaze above 1,100 degrees C. Besides, the results of XRF and Raman tests demonstrate that CaO amounts in the glaze decrease significantly with the increase in firing temperatures, which is the main factor to influence the Si-O linkages, adjust Q(1), Q(2), and Q(3-4) components, and modify the structure of the glass matrix during the firing process. The area ratios of the Si-O bending over stretching envelopes (A(500)/A(1,000)) of the glassy matrix have a negative correlation to the CaO amount. In contrast, the value has an apparent positive correlation to the firing temperature. The A(500)/A(1,000) value of the glass matrix increases from 1.29 to 2.40 as the firing temperature increases from 1,100 degrees C to 1,300 degrees C. These results prove that Raman spectroscopy could be used as a feasible and reliable nondestructive method to establish a more accurate relationship between Raman spectral polymerization index and the firing temperature in order to identify the firing temperature of ancient ceramics.