## 3 Results and Discussion
### Cuerda-Seca Decoration  
Concerning _cuerda-seca_ samples, we determined the composition of the black line which divided different areas of the drawing, and the glazes applied inside those areas. The analyses of the black lines showed inhomogeneous compositions (Table 5) that made it not realistic to establish average proportions. However, the high content of SiO\({}_{2}\) as major element in all the samples is remarkable, mixed with lead, manganese, aluminum, and iron. Manganese was the responsible for the black color of the line, probably in the form of different oxides. Lead could be added to enhance the adherence of the pigments to the paste [24], because the black line was applied directly on the non-fired paste, as can be deduced by the thickness of the interface (Figure 6). Figure 5: Monochrome colored glazes: (**a**) Secondary electron-SEM image of monochrome coating where a great interface between glaze and ceramic body can be observed; (**b**) Optical Microscopy image of a green glaze. The glazes used to fill the spaces between black lines were rich in silicon and lead (Table 5). The green glazes had tin oxide in lower proportions than white tin-opacified glazes. Although there were not many _cuerda-seca_ samples with yellow and green glazes among the studied samples, and the yellow ones showed great variation in lead content, the average composition of the PbO was similar to the secondary yellow/honey glazes (subgroup 2, Table 3) on green-and-brown decorated objects, and to green monochrome glazes (Table 4). However, the silicon proportion of _cuerda-seca_ glazes differed more in both colored glazes. Once again, the presence of copper and iron oxides with percentages around 2-3% contributed to the final color of the glazes. Only a sample showed _cuerda-seca_ decoration with honey and green-turquoise colors. In this case, the color was due to the presence of copper, but its green hue was shifted to turquoise because the glaze had alkaline-lead composition with a significant contribution of sodium (2.5% Na\({}_{2}\)O) and potassium (2.9% K\({}_{2}\)O) and lower lead content (23.3% PbO). These differences in green hues were already highlighted in _cuerda-seca_ ceramics of the 12 th century CE produced in the Iberian Peninsula [25]. Studies of pottery with _cuerda-seca_ glazes manufactured in the Iberian Peninsula during the 10 th-12 th centuries CE revealed the use of silicon and lead as main components [6; 24; 25]. The amounts of lead decreased from the 10 th century (43-55% PbO) to 12 th century CE (34-43% PbO), mainly in productions from the south of al-Andalus [25]. Nevertheless, samples manufactured during the 11 th century CE in the NE workshop of Zaragoza were characterized by high lead proportions [24]. Contrary to other types of decoration, pottery decorated with _cuerda seca_ produced in Albarracin in the 11 th-12 th centuries CE was more similar to the recipes employed in the south of the Peninsula with lead contents around 35-38% PbO. Figure 6: _Cuerda-seca_ decorated glazes: (**a**) Secondary electron-SEM image of the glaze; (**b**) Optical Microscopy image of _cuerda-seca_ decoration. Examinations by SEM of polished sections of _cuerda-seca_ glazes confirmed the presence of abundant inclusions scattered homogeneously in the glaze (Figure 6). The inclusion sizes varied from 50 to 70 \(\upmu\)m and their composition was mainly quartz. The use of such an amount of inclusions and their size, plus the tin-oxide content, could be responsible for the opacity. Opacification can be reached either with undissolved inclusions into the glazes or with tin-oxide crystals scattered in the glaze, and even with both of them [26; 27]. _Cuerda-seca_ ceramics manufactured in the same period in al-Andalus employed both techniques [6; 24; 25], although only tin oxide was employed as an opacifier in later centuries. Therefore, the inclusions found in the glazes played an important role in the opacity of the glazes.