## 2 Materials and Methods
### Experimental Field and Laboratory Trials with Herbicide Treatments
#### 2.3.2 Trials Performed in 1998 and 1999  
Two physical treatments, i.e., infrared and burning, and three chemical treatments, i.e., glyphosate (trade name: Roundup Ultra Plus, isopropylamine salt 36% _w/v_, Monsanto, Creve Coeur, MO, USA), sulphosate (trade name: Touchdown, trimethyl-salt with N-(phosphonomethyl)glycine 48% _w/v_, Syngenta Agro, Switzerland) and glufosinate-ammonium (trade name: Finale, glufosinate-ammonium 15% _w/v_, Bayer, Crop Science, Germany), each applied at 2.5% _w/v_, together with a wetting agent (nonylphenyl polyethylene glycol solution 20% _w/v_, Sigma-Aldrich, St. Louis, MO, USA, at 0.15% _v/v_) were tested in the first trial. Each treatment (Table 1) was applied to three test areas (1.5 m \(\times\) 2.5 m) in the outer face of the wall (15 test areas) and in the inner face of the wall (15 test areas), in the summer of 1998 (Figure 2b). One year later, in the summer of 1999, chemical treatments were again applied in the same test areas. Physical treatments were not repeated, as they gave rise to alterations in the materials (see result section). All test areas included schist with the three different degrees of weathering indicated in Section 2.2, mortar and scarce granite. There was no granite in those test areas where physical treatments were applied.  
In order to analyse possible modifications to materials due to herbicidal treatments, one piece of each type of masonry material (granite and weakly, moderately and strongly weathered schist) and one piece of mortar were selected in each test area. A portion of these pieces of approximately 8 cm\({}^{3}\) was obtained at different times: 17 days before and one year after the treatments, i.e., just before the re-application of chemical treatments (summer 1999). Five weeks after re-application, portions from the same pieces were collected.  
In addition, two representative, untreated pieces of schist masonry differing in colour and texture and two representative, untreated pieces of granite masonry, each of about 40 cm\({}^{3}\) and differing in colour and texture, were taken from the wall. Each piece was divided into three portions, and glyphosate, sulphosate and glufosinate-ammonium (the three chemical treatments) were applied (Table 1) in order to analyse surface colour modifications three months after the application.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Trial Date** & **Treatment** & **Preparation** & **Application in the Field** & **Application in the Laboratory** \\ \hline \multirow{4}{*}{Summer 1998 and summer 1999} & Infrared treatment (I) (B) (B) & \multirow{4}{*}{Not applicable} & At 2.5–3.5 bar pressure Application time: 10 min (I) and 1–2 min (B) & Not applicable \\  & Burn treatment (B) (B) & & & \\ \cline{1-1}  & & & & \\ \cline{1-1}  & & & & \\ \cline{1-1}  & Glyphosate (G) & \multirow{2}{*}{Not applicable} & For each chemical, an aqueous solution at 2.5\% & 20 mL/m\({}^{2}\) (G and S) & \\  & Sulphosate (S) & & _w/v_ plus the wetting agent & and 30 mL/m\({}^{2}\) (G-a) & \\  & Glufosinate-ammonium (G-a) & & _w/v_ & with a low volume & \\  & & & _w_hypernlypelythene & hand-held sprayer & \\ \hline \multirow{4}{*}{Spring 2016} & \multirow{2}{*}{Oxyfluorfen} & Aqueous solution at 0.5\% & 20 mL/m\({}^{2}\) of solution at 1.25\% _w/v_ with an ultra-low volume & Solutions at 0.5\% _v/v_, 1.25\% _v/v_ (3) and 100\% \\  & & & _v/v_, 1.25\% _v/v_, 100\% _v/v_ & ultra-low volume & \\  & & & sprayer (3) & _v/v_ applied by brush \\ \hline \multirow{4}{*}{Winter 2018} & _Origanum vulgare L._ & Aqueous solution at 2\% _v/v_ & 250 mL/m\({}^{2}\) with an ultra-low volume & \\  & _Thymus zygis_ Loefl. ex & plus the herbicide adjuvant & ultra-low volume & By brush (3) \\ \cline{1-1}  & L. _Thymus vulgaris_ L. & _Oil Orø_ at 2\% _v/v_ & sprayer (3) & \\ \hline \hline \end{tabular}
\end{table}
Table 1: Summary of the experimental field and laboratory trials with herbicide treatments.