## 3 Results
### Laboratory Assays with Glass-Based Historical Building Materials  
Laboratory experiments have the advantage of testing the damaging potential of a specific type of organism or group of organisms under controlled conditions. In the gathered literature these experiments use glass models with a chemical composition similar to historical samples. Not only chemical composition has been taken into account for the production of models, but some studies produced samples according to ancient technology. [PERSON] et al. [18] used blown glass since the effect of surface finishing can influence deterioration of glass. Studies regarding stained glass biodeterioration have been performed using K-rich, Mixed alkalis and Na-rich glasses (Table 3), the same glass compositions identified on the case studies (Table 2). K-rich glass was the most studied type of glass. Besides being widely used in stained glass production, it is also the most unstable type of glass so its conservation is a major concern [59]. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Material** & **Organisms** & **Time** & **Type of Silicate Glass** & **Alt. Products** & **Biodeterioration** & **Ref.** \\ \hline \multirow{4}{*}{\begin{tabular}{c} Stained \\ glass \\ \end{tabular} } & \multirow{4}{*}{Bacteria} & \multirow{4}{*}{6 w.} & \multirow{4}{*}{K-rich} & \multirow{4}{*}{Pristine} & \multicolumn{2}{c}{\begin{tabular}{c} Micro-cracking \\ Depletion of K, Ca, P and Na \\ on surface layer \\ Alteration Mn oxidation-state \\ \end{tabular} } \\  & & & & & & \\ \hline \multirow{4}{*}{\begin{tabular}{c} Fungi \\ \end{tabular} } & \multirow{4}{*}{6 m.} & \multirow{4}{*}{6 m.} & \multirow{4}{*}{K-rich} & \multirow{4}{*}{Pristine} & \multicolumn{2}{c}{\begin{tabular}{c} CaCO\({}_{3}\) \\ NaSO\({}_{4}\)-H\({}_{2}\)O \\ CaCO\({}_{3}\) \\ \end{tabular} } \\  & & & & & \multicolumn{2}{c}{CaCO\({}_{3}\)} \\  & & & & & \multicolumn{2}{c}{CaSiO\({}_{3}\)} \\  & & & & & \multicolumn{2}{c}{CaSiO\({}_{3}\)} \\  & & & & & \multicolumn{2}{c}{Hipphae fingerprint crystals} \\  & & & & & \multicolumn{2}{c}{Aeration elements depletion} \\  & & & & & \multicolumn{2}{c}{} \\  & & & & & \multicolumn{2}{c}{} \\  & & & & & \multicolumn{2}{c}{} \\  & & & & & \multicolumn{2}{c}{} \\  & & & & & \multicolumn{2}{c}{} \\ \hline \multirow{4}{*}{\begin{tabular}{c} Fungi \\ \end{tabular} } & \multirow{4}{*}{40 d.} & Colourless & \multirow{4}{*}{} & \multirow{4}{*}{\begin{tabular}{c} CaCO\({}_{3}\) \\ \end{tabular} } & \multirow{4}{*}{\
\begin{tabular}{c} Glass higher stability present \\ superficial biofilm and glass \\ with low chemical stability 3D \\ growth of the biofilm \\ \end{tabular} } \\  & & & & & \\ \hline \multirow{4}{*}{
\begin{tabular}{c} Fungi \\ \end{tabular} } & \multirow{4}{*}{5 m.} & Colourless & \multirow{4}{*}{} & \multirow{4}{*}{Pristine} & \multicolumn{2}{c}{Hidescent stains} \\  & Na-rich & & & \multicolumn{2}{c}{crystal formation} \\  & & & & & \multicolumn{2}{c}{} \\  & & & & \multicolumn{2}{c}{} \\  & & & & \multicolumn{2}{c}{} \\  & & & & \multicolumn{2}{c}{} \\  & & & & \multicolumn{2}{c}{} \\ \end{tabular} } \\  & & & & & \multicolumn{2}{c}{} \\ \end{tabular}
\end{table} 
Table 3: Laboratory experiments performed on glass or glaze models to simulate stained glass and glazed tiles biodeterioration. Time in \(w\) means weeks, \(m\) means months and \(d\) stands for days. The alteration products and biodeterioration patterns are also on this table. Regarding glazes, only lead-alkali glaze opacified with tin was used in the laboratory experiments; no study was performed with transparent lead glazes. White opacified glazes are very common in glazed tiles production, as for many centuries they were used exclusively in Dutch, Portuguese, Spanish, and Italian glazed tile manufacturing. The laboratory-based experiments used the same glaze composition with two different conservation states: pristine and aged. The effect ageing has also been tested for stained glass by using pristine and corroded glass samples [18].