## 3 Results and Discussion
### Clustering  
Figure 6 shows the resulting segmented images after applying k-means clustering to the thermal data cube of the reflection mode measurement, with, from left to right, a gradual increase in the number of clusters. When k = 2 clusters, the glass panes are distinctively separated into two groups, in a similar way as can be visually seen in the thermogram at the start of cool-down process (see Figure 3). Aside from the smaller panes near the top, which are heavily influenced by the lead cames, no additional panes or distinct parts of the panes are segmented when k = 3. An additional group of  
Figure 5: **Top row: the red lines in the reflection mode thermograms are line scans, indicating the position of the pixels for which the values are displayed in the graph. Bottom row: the graphs show the temperature difference at different times of cooling-down averaged over 3 pixels. Temperature differences are normalized over the entire data cube. The lead cames heavily influence the temperature behavior of the surrounding glass. The larger glass panes (left) have an area that remains unaffected but this is not the case for the smaller glass panes (right). **  
glass panes seems to emerge at the right side of the window when k = 4 (indicated in cyan in Figure 6) and is distinctly separated when k = 5. This group corresponds to the glass panes that could be visually discerned as fragments with a faster cooling in the thermogram recorded two minutes after heating (Figure 3, 2 min of cooling). Since these panes are only segmented at higher values of k, this group differs less from the other panes compared to the group indicated in red. The top left corner of one of these panes (indicated with an orange frame in Figure 6 at k = 5) appears to behave differently, as also seen in the thermograms. In the images of the lower region, the glass pane in the top left corner is separated from all other panes for k = 4 and k = 5 clusters (indicated in yellow). This pane does not get separated in the images of the upper region. The small piece of glass in the top row that behaves differently in the thermograms (Figure 3, start of cooling) does not seem to get segmented in the cluster analysis. These results look similar to what we found while examining the individual thermograms, with some exceptions for smaller pieces. Figure 7 shows the dendrograms as a result of hierarchical clustering on the averaged ROIs. Starting from each individual observation, the observations are linked together into larger clusters. These links are depicted by the horizontal lines in the dendrogram. The position of this line on the y-axis indicates the distance between the linked groups. Starting from the top of the dendrogram, and working towards the bottom, we can split up the formed clusters into subsequently smaller and smaller clusters. Determining the correct amount of clusters is a somewhat arbitrary process. The corresponding ROIs are indicated by the red frames on the images on the right sides of their respective dendrogram. When evaluating the dendrogram of the upper region, the first three clusters (red, magenta + green and red) seem to correspond to the same groupings of glass pieces we found with the other methods. Cutting the dendrogram into four clusters, i.e., splitting the magenta and green branches, places ROI 2 and ROI 3 in different clusters, but otherwise does not yield any additional insights. This is because the red cluster encompasses the smaller glass panes, which are heavily influenced by the surrounding lead camps. If we cut the dendrogram of the lower region into four clusters, we arrive at the same groupings of glass panes we found with the previous methods. ROI 34 is placed into a different cluster from the other ROIs that are part of this group. This is in accordance with what we see in the thermograms and k-means results. The ROIs from the glass pane in the top left corner (ROI 26 and ROI 27) are placed in a completely separate cluster from the other window panes in the bottom image.