## 3 EM Techniques for CH Diagnosis
### Microscopy
#### 3.1.3 Practical Application of Microscopy to CH  
Understanding the capabilities and limitations of microscopy is essential for effectively analyzing cultural artifacts. As detailed in Table 6, incorporating quantitative information on resolution and other constraints provides clearer insights into the strengths and appropriate applications of various microscopy techniques. Including precise resolution, data not only facilitates informed method selection but also enhances material characterization and the development of targeted preservation strategies [88; 89; 90; 93; 94; 95; 96; 97]. \begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt}} \hline \hline \multirow{4}{*}{Light Microscopy} & **Resolution Limit:** Approximately 200 nanometers (nm) \\  & **Details:** \\  & Based on the diffraction limit described by Abbe’s equation. \\  & Suitable for observing larger cellular structures, organelles, and tissue architecture. \\  & **Limitations** include the inability to resolve structures closer than \(\sim\)200 nm due to diffraction. \\ \hline \multirow{4}{*}{Electron Microscopy (EM)} & **Transmission Electron Microscopy (TEM):** \\  & **Resolution:** Up to 0.1 nm (sub-angstrom level) \\  & **Capabilities:** Visualizes ultrastructural details within cells, such as macromolecular complexes. \\  & **Limitations:** Requires extensive sample preparation, vacuum environment, and thin sectioning. \\  & **Scanning Electron Microscopy (SEM):** \\  & **Resolution:** About 1–10 nm \\  & **Capabilities:** Provides detailed 3D surface morphology. \\  & **Limitations:** Limited to surface features; sample must be conductive or coated. \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Quantitative Comparison of Microscopy Techniques’ Resolution Capabilities and Limitations. \begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**Technique** & **Data/Information** & **Limits** \\ \hline Light microscopy 2 & Surface 1 information & Limited focus depth \\  & Morphology, & The fibrous material may undergo charging effects, leading to overexposed images \\  & Crystallographic information & \\  & Elemental composition & \\  & Chemical speciation & \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Summary of microscopy’s main characteristic with respect to CH applications, according to the literature reviewed 1. A comparative overview focused on the cost-effectiveness and accessibility of each microscopy technique is summarized in Table 7[88; 89; 90; 93; 94; 95; 96; 97]. Regarding microscopy applications, we present an example from the less-studied area of metal objects. In [69], [PERSON] addresses the use of reflected light microscopy (RLM) and scanning electron microscopy (SEM). The first has been used to examine polished surfaces of metal samples (axes, sickles, spears, and swords), both before and after etching with alcoholic ferric chloride. We quote their exact words because they clearly explain how microscopy may be applied and what it can reveal: \"Observations before etching provide information on the state of preservation and corrosion penetration, metal inclusions, and porosity. Etching revealed the nature of the dendritic and granular structures, including shape, size, and characteristics of the dendrites and grains [...] and the positioning of inclusions within the metal matrix\" [69] (p. 4). Regarding SEM, they use it for semi-quantitative identification and additional imaging, combined with energy dispersive spectrometry (EDS). In [102], the use of microscopy is indicated for analyzing degradation factors in stones, particularly calcium oxalate films, lichens (often the main cause of calcium oxalate formation), and plants. Since this issue mainly concerns outdoor monuments, which are not the focus of this work, we mention it only for completeness. Microscopy is a traditional, well-established technique and has been used even for the Salvator Mundi of [PERSON] in 2011.