## 4 IRT Different Case Studies from Diagnosis to Protection Interventions
### Assessment of Conservation Interventions
#### 4.3.4 Evaluation of Protection Interventions  
The historic building of National Archaeological Museum (NAM) is located in the centre of Athens, and it was constructed in 1889. The western (main) facade of NAM consists of several types of plasters and pentelic marble surfaces (Figure 19). During the diagnostic study performed for the characterization of building materials and decay diagnosis, the purple masonry historic plaster, which is located on propylaem and galleries of the main facade, was examined [29].  
The plaster under investigation was of marmorino type (lime binder with fine grained calcite aggregates), and its purple colouring was attributed to the natural earth pigment of Fe\({}_{2}\)O\({}_{3}\)[30]. However, major discolorations were observed all over the purple plastered architectural surfaces of the NAM propylaem and galleries because of the poor preservation state of a coating applied during previous protection interventions. Digital microscopy was applied on the plastered surfaces under investigation, demonstrating that, at some areas of the plastered surfaces, the protective coating was firmly attached to the substrate (Figure 20, top row, left), while at other areas, the coating was friable, loosely attached to the substrate, and presented a whitish hue (Figure 20, top row, right). Furthermore, in many cases, the protective coating was fractured and detached from the substrate, presenting a yellow hue (Figure 20, low row, right and left).  
Figure 19: Facade of the National Archaeological Museum of Athens: The blue box indicates the plastered area of propylaem, investigated by IRT.  
Figure 18: Thermal image of Kapandriti’s stone surface.  
IRT investigation (AVIO TVS-2000 Mk II LW, 8-12 \(\upmu\)m) took place when no direct sunlight was affecting the plastered architectural surfaces (Figure 21, environmental conditions: T = 22.5 \({}^{\circ}\)C, RH = 53%). It was shown that the areas of fractured, detached, friable and loose coating presented higher temperatures (from 24.2 \({}^{\circ}\)C to 25 \({}^{\circ}\)C) compared with areas of firmly attached coating (temperature readings from 21.73 \({}^{\circ}\)C to 22.53 \({}^{\circ}\)C). In particular, the areas where the protective coating is fractured and detached from the plaster are depicted by yellow and red colours, while the areas of friable and loosely attached coating are rendered by purple colours. The areas displayed by blue and black colours correspond to the coating firmly attached to the plaster.  
This non-uniform temperature distribution is attributed to moisture withholding because of the protective coating application (a material of organic composition) that constrained the substrate transpiration, which affected its vapour permeability. Therefore, in addition to the inspected discolorations, the applied protective coating presented physicochemical incompatibility to the substrate. During the planning phase of the conservation interventions on the NAM's architectural surfaces, the decision was made to remove this coating.  
Figure 21: Plastered area under investigation and corresponding IRT image.  
Figure 20: Digital microscopy images displaying the different preservation states of the protective coating applied on the plastered surfaces.