## 3 Results
### Predicting Chemical Composition  
The random forest model was used to analyze the chemical compounds within the high-potassium and lead-barium glasses and identify the sensitive element changes that occurred due to weathering. As shown in Figure 4, for high-potassium glass, the top six significantly altered chemicals affected by weathering were K\({}_{2}\)O, Fe\({}_{2}\)O\({}_{3}\), SiO\({}_{2}\), Al\({}_{2}\)O\({}_{3}\), CaO, and P\({}_{2}\)O\({}_{5}\), with importance indices of 0.55, 0.41, 0.37, 0.27, 0.20, and 0.17, respectively. Other components such as MgO, CuO, PbO, and BaO were almost unchanged with importance indices lower than 0.03, indicating that the contents of these chemical substances were influenced by weathering. For lead-barium glass, the top five significantly altered chemicals affected by weathering were SiO\({}_{2}\), PbO, CaO, Al\({}_{2}\)O\({}_{3}\), and BaO. Among them, the importance indices of SiO\({}_{2}\), PbO, and CaO were many times higher than that of the other chemical components, with importance indices of 0.41, 0.34, and 0.33, respectively. In addition, the importance indices of the other components such as K\({}_{2}\)O, PbO, MgO, Fe\({}_{2}\)O\({}_{3}\), and SrO were negligible, indicating that these components were very stable and were not changed by weathering. Therefore, the components that are sensitive to weathering could be effectively utilized to determine the weathering status of glass artifacts.  
The pre-weathering chemical compositions of glass artifacts containing high-potassium and lead-barium were forecasted by the BP model and are presented in Figure 5. According to Figure 5, the average chemical composition of each sample of predicted weathered high-potassium glass and lead-barium glass was obtained. A comparison was conducted between the average chemical composition after weathering and the original composition, yielding the rate of change for each chemical component after weathering. For the high-potassium glass, the chemical contents of K\({}_{2}\)O, Fe\({}_{2}\)O\({}_{3}\), Al\({}_{2}\)O\({}_{3}\), CaO, and P\({}_{2}\)O\({}_{5}\) were decreased by 95.3%, 76.3%, 72.2%, 81.1%, and 55.9% after weathering, respectively. Contrarily, only the content of SiO\({}_{2}\) increased after weathering, by 32.1%. In addition, the contents of the other chemical components were hardly changed. The results indicated that weathering was highly corrosive to high-potassium glass, and the main chemical components were largely converted into SiO\({}_{2}\). In contrast, after weathering, the lead-barium glass samples experienced a decrease in SiO\({}_{2}\) (30.4%) and CaO (18.8%) and an increase in PbO (42.2%), Al\({}_{2}\)O\({}_{3}\) content (10.2%), and BaO content (21.2%). Consequently, the variability in the chemical components showed that that the lead-barium glass experienced relatively limited erosion and minor alterations in SiO\({}_{2}\) content following weathering compared with high-potassium glass. The results were consistent with the reports shown in Figure 4, indicating that the chemical composition, greatly affected by weathering, exhibited significant changes before and after weathering for both glass types.  
Figure 4: Weathering-induced changes in chemical composition of two glass types.