# Terahertz Inspection of Buildings and Architectural Art
## 4 Monitoring of the Conservation Process of a Mural  
An original study that we present as part of this contribution is the evaluation of the restoration process of the mural paintings of the Konstantinbasilika (The Basilica of Constantius). The Basilica was built in the III and IV centuries by the Roman emperors [PERSON] (293-306) and [PERSON] (306-337) as a reception hall of the imperial palace. This large Roman building has evolved from being a castle to episcopal residence and protestant church (since 1856). On it, remain some of its colorful Roman facade decorations, primarily found in the window reveals. As part of a varied history, the Konstantinbasilika has undergone many architectural changes. During the restoration of the building in the XIX century, the remaining Roman plaster and painting fragments of the facade were uncovered. Only a few connected plastered areas survived to this day. This includes larger original plasterwork in the northeast. They show a warm, flat white tone with dividing painting elements in an intense red. In addition, larger painted surfaces, including remains of floral and figurative decoration, have been preserved in the window reveals of the west side and the apse [47]. These paintings have been exposed to weather deterioration since the XIX century. Yet, different efforts have been made to prevent the deterioration of the paintings as a consequence of color weakening, pigment alteration, mainly owing to the formation of black crusts (sulfation) and the accumulation of dirt as well as climate variations and wind-related erosion. A series of potential restoration/conservation strategies were evaluated for these mural paintings. It was decided to apply a removable protective cover in order to protect them against further deterioration. A fundamental consideration for this decision was the fact that existing climatic influence on the surfaces can often only be effectively reverted to a limited extent. A protective removable cover, on the other hand, represents an alternative that can preserve the artwork on the long term. The concepts for covering wall paintings for conservation purposes were developed in Germany in the nineteen hundreds, but a systematic follow-up and examination of various techniques is currently a topic of debate and active research. An effort aiming to contribute to this discussion is promoted by some research projects at the Department of Conservation and Restoration of Wall Painting and Architectural Surface of HAWK in Hildesheim, in collaboration with the federal state Rhineland-Palatinate and the Directorate-General for Cultural Heritage. A specific objective is to further develop, adapt, and optimize conservation measures, such as long-term protection of weather-exposed surfaces. For our investigation, we selected an area of the mural of the Basilica, which was in the process of being covered; this section lies on the west facade and was intervened in 2016. The conservation system was used at the Konstantinbasilika, as shown in Figure 6. The original mural paint was covered by a cyclodotodecane (C\({}_{12}\)H\({}_{24}\) ) layer, then a reinforcement with para-aramid fibres (KEVLAR) was placed and finally the sacrificial render layer, made of Roman cement, was applied. Cyclodotodecane was chosen as the separating layer, because it temporally seals the historical surface but subsequently sublimates without leaving traces on the original artwork. Depending on the processing temperature and the addition of benzine, molten cyclodotodecane can be applied on a relatively thin layer in order to better match the shape of the covering plaster to the original historic surface. After sublimation, it is assumed that a thin air-gap remains between the original artwork and the new reinforced plaster. In an early series of investigations on the first sample area at the Konstntinbasilika in 2015, a destructive examination of the sublimation of cyclodotodecane was carried out. A circular drill was used to cut an area from the surface of the protective plaster.