## 3 Results and Discussion  
### Thermograms  
By examining the thermograms at the start of the cool-down process (Figure 3, left column), we can clearly distinguish two different glass types. In particular, there are three glass panes that display a lighter grey value because they heat up faster than the other fragments. These panes have a slightly greener hue than the other panes (Figure 1), indicating the presence of chromophores. The added absorption by these chromophores might be the cause for the higher temperature of these glass panes. [PERSON] et al. also observe higher temperatures for coloured glasses compared to colorless glass due to the presence of chromophores [20]. There is also a small triangular glass fragment in the top row that behaves differently from the surrounding glass, while it has the same visual color. After two minutes of cooling-down (Figure 3, right column) the same glass panes stand out in the thermograms but an additional type of glass appears to emerge. These four panes, indicated by red frames in Figure 3, appear to cool down faster and thus exhibit darker grey values than the other panes. In general, the thermal behavior of the glass panes is similar in transmission and reflection mode. Damage on the surface of the glass panes from scratches and glass corrosion is much more visible in the transmission mode measurement, as can be seen in Figure 4. Glass areas subjected to degradation seem to heat up more, as reported earlier by [PERSON] et al. [22] Although the impact is limited here, this can become problematic when windows are considered with a higher grade of weathering. Therefore, it seems more favorable to employ a reflection mode measurement when IRT experiments are carried out with the specific purpose of distinguishing different types of glass. In addition, the contrast between the lead canes and the surrounding glass is less pronounced in transmission mode. Figure 4: Comparison of the reflection (**left**) and transmission (**right**) mode at the start of the cooling-down process. Scratches and corrosion is more prominent in transmission mode. Figure 3: Reflection mode thermograms of the upper (**top** row) and lower parts (**bottom** row). **The left column** shows the window at the start of cooling, **the right column** after 2 min of cooling. The upper and lower images have one row of glass panes in common. Two types of glass can be discerned in the image before cooling, while the red line indicate a possible third group that emerges in the image during cooling. The temperature difference is measured with respect to the average cold frame. The lead cames appear to heat up much faster than the glass and they heavily impact the thermal behavior of the surrounding glass. We examine this effect for two line scans in Figure 5: the scan on the left covers a row of the larger glass panes, while the scan on the right covers the row of smaller panes near the top of the window. The larger glass panes in the lower half of the window have an area in the center that remains largely unaffected by the influence of the lead cames, but this is not the case for the smaller glass panes near the top of the window. As a result, it will be difficult to determine whether differences and/or similarities are actually caused by a difference in chemical composition of the glass or rather by the influence of the lead cames. The lead cames appear to cool down much faster than the other elements, and over time their influence on the surrounding glass diminishes. A narrow area next to the wooden frame also displays a noticeably lower temperature difference. This can be seen in the outer edges of the temperature plots (Figure 5) and the thermograms (Figure 3). We suspect this is caused by non-uniform heating due to the window frame casting a shadow on this area. Since the effects of glass degradation are more apparent in the transition mode measurements, this data is deemed less reliable. Therefore, the reflection mode measurement data is used for clustering.