# Characterization of Ancient Marquetry Using Different Non-Destructive Testing Techniques
## 6 Discussion  
Among the three NDT methods applied in this study, it is clear, based on the results and previous works widely available in the literature, that X-ray micro tomography provides clearer and more precise results. As it can be observed in Figure 6, it provides the best sensitivity revealing with detail porous delaminations and cracks both in the tessellatum and wooden parts as discussed in Section 5.2. However, it is also the most expensive test to be performed and it is not easy to apply it outside the laboratory. Thus, it is not always the method of choice for inspection of cultural heritage objects since the object to be inspected is often in its original place and can not be moved.  
Figure 7: PCT results obtained from infrared sequences. (**a**) Second EOF from MWIR, **(b)** third EOF from MWIR, **(c)** second EOF from LWIR, and (**d**) third EOF from LWIR.  
Cultural heritage inspections usually involves very sensitive material. Because of that, in most cases, ultrasound inspections are not applied due to the need of a coupling agent. On the other hand, air-coupled UT does not require this coupling agent which makes it a perfect candidate for inspection of cultural heritage artifacts. In Section 5.1, some results using this technique were presented. The darker lines shown by arrow in Figure 5a for instance are probably related to the wooden texture present underneath the decorative parts which indicates that the wooden texture plays an important role for the amplitude contrast of Air-UT inspection for this kind of sample. In addition, based on surface materials visible in Figure 1 and bright areas visible in Figure 5a, one can assume that bright areas are likely related to delaminations. However, due to low contrast (Figure 5b) this method is not the best candidate for NDT inspection of marquetry samples.  
Finally, infrared thermography combines more interesting results (when compared to Air-UT) with a cheaper setup (when compared to micro-CT). For example, the bright areas that are depicted in Figure 5a are also distinguishable in the IRT results. One example are the ornaments in the orange circle in Figure 7a that coincide with bright areas in the Air-UT results. Additionally, the red circles shown in Figure 7b highlight two different ornaments made with the same material (Figure 1) that present different colors from its similar ornaments (in other places of the sample). This indicates that some defect is present in the regions indicated by the red circles. Another example are the regions indicated by the green arrows (Figure 7b). In the visible image, the ornaments look the same, but in the IRT image, they present different colors, which leads us to conclude that the region pointed by the second green arrow (in the right portion of the image) has a delamination. The yellow arrow in the same IRT result image indicate a crack in the tessellatum which shows that, similarly to the micro-CT results, it is also possible to detect cracks with IRT. In addition, among the three NDT techniques that were applied, IRT is cheaper and very easy to deploy on site, which makes it the more attractive technique. Table 1 summarizes the main differences found among the three different NDT methods used in this study.