# A Survey of Electromagnetic Techniques Applied to Cultural Heritage Conservation
## 3 EM Techniques for CH Restoration  
Decontamination and consolidation are the most relevant conservation/restoration treatments used to recover and extend the integrity of a CH artifact over time, and these can be performed using EM techniques. For this type of application, the most authoritative  
\begin{table}
\begin{tabular}{c} \hline
**EM Irradiation for Restoration** \\ \hline Gamma/X-ray \\ Radiofrequencies \\ Microwave heating \\ \hline \end{tabular} \({}^{\dagger}\) By restoration, we mean decontamination and solidification.  
\end{table}
Table 2: EM techniques for CH restoration \({}^{1}\) covered in Section 3.  
reference source is the International Atomic Energy Agency (IAEA), as the techniques used are based on ionizing radiation. Radiation techniques consist of EMWs or charged particles irradiating the artifact and interacting with its matter in different ways [14]. In the case of EMWs, the important factors during the irradiation process are as follows:  
* Irradiating photon energy;
* Atomic number of the absorbing material.  
Because the atomic number of the absorbing material is a key parameter in the irradiating process, it follows that these techniques do not yield to the same result on different materials. According to the state of the art reached in France over more than 50 years of experience in the field [8], and to the information provided by the IAEA [14; 87], artifact types for which radiation treatment are not recommended are glass, gemstones, amber, basketworks, bone, horn, ivory, and tortoiseshell. On the opposite site, materials for which radiation treatments are most successful are all kinds of wood and paper artifacts, composite ethnographic collections, natural history collections, and mummies. Concerning photographs and film stock, the suitability for radiation techniques depends on the substrate material and, in the case of cellulose nitrate or acetate, these techniques must be avoided.  
Although different treatment typologies exist (see Table 3), all ionizing radiation produces chemical effects in the irradiated material by breaking the chemical bonds. In fact, \"ionizing radiation is a radiation with enough energy to remove tightly bound electrons from the orbit of an atom, causing that atom to become charged or ionized\" [88]. Covulent bonds, typical of living creatures and organic materials, are the most affected ones. Irradiation affects important parts of the DNA structure; it actually acts in two main ways:  
* Direct interaction with the DNA;
* Indirect modification, inducing free radical production through water radiolysis [59].  
A _rule of thumb_ to keep in mind is that the more complex the organic molecules are, the less energy is required to damage them and eventually inhibit their replication [14]. This means that dose required to decontaminate CH objects from insects is lower than the one required in the case of mold; the dose range usually used for insect eradication is 0.5-2 kGy vs. a dose of up to 10 kGy for mold. A second major aspect to outline is that some biodeteriogens are not only dangerous for artifacts, but are also toxic to humans [86], while irradiated materials do not retain radiation; hence, they cannot irradiate people working on them after treatment, nor visitors.  
Since the techniques investigated in this section are strictly related to how the deterioration of CH artifacts begins and evolves, you may refer to Section 4 for an insight into the main causes and principal processes leading to CH deterioration.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Methods** & **Principles** \\ \hline Mechanical 1  & Physical removal of pathogen factors \\ Chemical & Elimination of pathogens by chemicals \\ Biological & Bio-cleaning/bio-mineralization through microorganisms \\ physical & Based on anoxic treatments \\ \hline \hline \end{tabular}
\end{table}
Table 3: Main disinfection methods and their principles.