# The Influence of Raw Materials on the Stability of Grisaille Paint Layers
## 2 Materials and Methods  
### Samples Preparation  
To better understand the influence of the raw materials on the stability, different grisailles were produced and compared, changing one variable each time, showed in Table 1. The variables considered were the coloring agents, base glass, vehicles and other materials, the firing temperature, the proportions between the components, and the glass support (Table 1). \begin{table}
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**Variables** & \begin{tabular}{c} **Coloring** \\ **Agents (CA)** \\ \end{tabular}  & **Base Class (BG)** & \ \begin{tabular}{c} **(CA-BG)** \\ **wt\%** \\ \end{tabular}  & **Vehicle** & \begin{tabular}{c} **Other** \\ **Materials** \\ \end{tabular}  & **Substrate Class** & **Temp. ** & **Image of Final Grisaille \\ \hline \multirow{4}{*}{Other materials} & Iron and copper (1:1 wt\%) & \multirow{2}{*}{Roaille} & (1:1) &  
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The initial grisaille (Model grisaille) formulation agrees with the most common raw materials identified in the historical treatises [2]. It was made by mixing burned iron and burned copper (1:1 wt%) as coloring agents, rocaille (SiO\({}_{2}\) + PbO (1:3 wt%)) as base glass, gum arabic (0.1 wt%) and water as temporary binder and vehicle. The base glass and the coloring agents were used in a 1:1 wt% ratio, painted on the non-tin side of commercial glass slides (Deltalab(r)), following the paint application methodology from [PERSON] et al. [3], and fired at 650 \({}^{\circ}\)C. A total of 26 grisailles were produced, changing one of the variables each time (see Table 1). Practical grade (PA) reagents were used for some raw materials. All the brands and manufacturers of the commercial PA reagents are described in Appendix A.  
Low-carbon steel and standard copper plates were used to obtain the burned iron and copper. Both metals were cut into small pieces and placed in crucibles in an electric furnace, during two heating cycles, to a maximum temperature of 850 \({}^{\circ}\)C for 1 h, promoting metal oxidation. Afterward, both metals were grounded into a fine powder for 5 and 10 min. The SiO\({}_{2}\) and PbO for the base glasses were mixed in different proportions (Table 1). After 10 h of melting in an electric furnace (BARRACHA-model E6) at 1100 \({}^{\circ}\)C in ceramic crucibles, the mixtures were poured into water, dried, and grounded in an electric agate mortar. Different substrate glasses were produced (Table 1) according to the compositions of the most common glasses from historical stained-glass windows [17]. They were melted in an electric furnace (TERMOLAB-BL) at 1400 \({}^{\circ}\)C for 3.5 h in ceramic crucibles and blown into the form of a rounded using the same procedure as the historical production of crown-window glass. Most of the other materials added were practical grade reagents, except for the burned tin and lead and the lead white. The burned tin and lead were produced according to the descriptions from historical recipes; lead oxide (PbO) and tin oxide (SnO\({}_{2}\)) were mixed in a 1:1 wt% ratio and burned at 900 \({}^{\circ}\)C for 2 h. This burned lead and tin was also known as a lead-tin-yellow pigment, widely used in oil painting [18]. The lead white pigment used was produced by exposing metallic lead to acetic acid (vinegar) [18]. The other materials (alumina, antimony, burned lead and tin, burned lead, and lead white) were added to the grisailles in proportions of 1:1 wt% with the coloring agents. Moreover, the sum of the coloring agents and the other materials was 1:1 wt% with the base glass. Leaving grisailles with 1:1:2 wt% proportions between the coloring agents, other materials, and base glasses. These ratios were chosen according to the quantities described in the historical recipes with these materials in their composition [2].