# A Survey of Electromagnetic Techniques Applied to Cultural Heritage Conservation
## 2 EM Techniques Applied to CH  
In this paper, with the term CH, we refer to tangible cultural heritage, and we consider those objects that have been highly damaged by natural causes (pest attacks, floods) or wars, as well as artifacts subjected to intense use, buried, and under water. Our focus is on the EM techniques applied to conservation/restoration of CH, meaning by conservation/restoration the direct interventions to extend the lifetime or to recover the integrity of CH artifacts, and considering as EM techniques those based on ionizing radiation produced with electromagnetic waves (EMWs). The techniques presented are those that have proven themselves to be efficient yet safe. Table 1 summarizes the most consolidated techniques at the moment, their applications, and the main references reviewed. We do not intend to provide a complete and in-depth knowledge of each technique but rather to offer a preliminary understanding that may serve as a starting point for further and more detailed studies on the matter. Each technique will be investigated based on its physical principles; this approach provides immediate comprehension of the results that may be achieved through its application, the materials/artifacts to which it is best suited, and its advantages and limitations. At the base of the various techniques we will consider, there is the interaction between matter and EM radiation, which is the principle underlying both diagnosis and restoration [48]. As anticipated in the Introduction, the first attempt to apply Science to Cultural Heritage occurred for diagnosis purposes. The first countries to embrace the challenge in the first half of last century were France, Germany, and the USA, while in Italy, there was mostly resistance to the application of scientific methodology and techniques in the field of CH [49]. In the USA, scientific and innovative research was already conducted in the 1920s-1930s at the Fogg Art Museum at Harvard University [50], and at the time, Munich (Germany) could already boast a century of activity [51]. The first country that considered the application of EM radiations for conservation purposes was France. [PERSON], director of the laboratory established at the Louvre in 1923, during the first International \begin{table}
\begin{tabular}{c c c} \hline \hline
**Technique** & **Application** & **References** \\ \hline Gamma/X-ray/ion beam irradiation & Decontamination of: & \\ wood & [10; 22; 23] \\  & parchment & [26; 27] \\  & paper & [11; 15; 16; 17; 36] \\  & textile & [30] \\ Gamma irradiation & Wood consolidation & [14; 37] \\ Microwave (MW) heating & Decontamination of: & \\  & Stone & [38; 39; 40] \\  & wood & [41; 42; 43; 44] \\ Radiofrequency (RF) & Biofilm removal & [45; 46; 47] \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Irradiation techniques of wider application for decontamination/consolidation purposes and relative most relevant references. Conference for the Study of Scientific Methods in the Examination and Conservation of Artworks (Rome, October 1930), brought to attention the conservation issue together with the diagnostic one; in particular, he spoke of the possible treatment of wooden states against parasites and of precautions to be taken for stone artifacts against atmospheric agents, as well as precautions to preserve artworks from ventilation, heating, and illumination in the exhibition rooms [49]. Since our focus in this paper is on EM technique for conservation/restoration of CH artifacts, we are not interested in the science of spectroscopy, which is mostly related to diagnostic applications. For an overview of this science, the interested reader may refer to publications [52; 53; 54]. However, spending a few words on spectral absorption is due. The father of atomic absorption is [PERSON] [55; 56; 57]. In his famous paper [58], he outlined the relevance of absorption in determining the concentration of an element.