## 3 Results
Artificial soiling was carried out under forced conditions, using hard bristle brushes with flat tips, so that the mixture adhered to the surface and between the interstices of the weave [9]. The amount of mixture deposited was about 1 g for each mock-up sample and was determined by weighing the sample before and after application of the mixture with the brush. Cleaning tests were also performed on mock-up samples (Figure 4) in order to quantify the deposited particulate material (DPM). It is interesting to note that among the various methods used, the one capable of removing the greatest amount of DPM was immersion washing (Figure 5), although it should be noted that this technique is the most invasive. The method based on hydro-aspiration is the second most more effective one. To confirm the correctness of the observations made on the efficiency of the methods, it can be noted that the trend of the quantity of DPM removed is the same on the tapestry and mock-up samples, as reported in Figure 5.  
Figure 4: An example of the cleaning operations: hydro-aspiration and air aspiration methods. On the right side some examples of selected areas submitted to cleaning are shown together with the same two methods applied on some mock-up samples. Figure 5: DPM quantity (mg) collected on quartz fibre filters by means of the different cleaning procedures on selected areas (3 \(\times\) 3 cm\({}^{2}\)) of mock-up samples (**a**) and on selected areas from the ancient tapestry (**b**). The morphological characterisation of the surfaces of the quartz filters was performed by means of SEM-EDX analysis. For each sample, a 1 cm\({}^{2}\) punch, which visually showed a higher dirt accumulation, was obtained, placed on the sample holder and analysed. For each cleaning method used, the filters collected after 1.5 min and 5 min samplings were analysed. In Figure 6a,b the SEM images of filters collected after 1.5 min and after 5 min together with the corresponding EDX analyses, as regards method A (hydro-aspiration), are shown. The presence of silver and sulphur allows us to assume that the particles are composed of silver sulphide attributable to the degradation of the wire. This finding puts in evidence that the cleaning method applied tends to remove the sulphide flakes that, more or less compactly, cover the metal surface. However, it is interesting to note that when analysing the filter collected after 5 min (Figure 6b), the amount of silver is lower (Table 1): 9.3% compared with 17.3% found on the filter collected after 1.5 min. This means that we can assume that no further silver-containing particles are removed after the first cleaning step. It is worth noting that Si is mainly due to the quartz filter, even if a contribution due to the soil dust deposited on the tapestry surface cannot be excluded, also because of the presence of Al and Ca, elements typical of aluminium calcium silicates. They are among the constituents of the aerosol particulate matter that can be deposited on the works of art. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Element (Weight \%)** & **Si \({}^{*}\)** & **S** & **Ag** & **Al** & **Ca** & **Cl** \\ \hline Area a (1.5 min) & 53.9 & 2.6 & 17.3 & 2.1 & 5.0 & 14.1 \\ \hline Area b (5 min) & 72.6 & 1.4 & 9.3 & 0.8 & 3.9 & 11.9 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: EDX analysis acquired on area a (a) and area b (b). \({}^{*}\)Si is mainly due to the quartz filter. The precision of the results reported is 5%. Figure 6: SEM images and the corresponding EDX analyses acquired on quartz fibre filters by method A (hydro-aspiration) after 1.5 min (**a**) and 5 min (**b**). It is worth noting the comparison of method A with the other cleaning procedures. For example, analyses carried out on the filter collected by method C (lower pressure-table) after 1.5 and 5 min also revealed numerous particles containing sulphur and silver, as shown in Figure 7a,b. Method C appears to be rather invasive as evidenced by the larger size of the silver sulphide particles removed.