*3.3. Monochrome Colored Glazes*

Colored glazes were used for coating always both ceramic sides. Yellow/honey glazed samples were decorated on both sides of the objects with the same color; however, green glazed fragments were decorated with either green or yellow glazes on the secondary side. Compositional analyses of green and yellow monochrome glazes (Table 4) revealed that they were rich in lead and silicon, with minor quantities of iron, aluminum, calcium, and alkali oxides. Similar chemical compositions were determined on the secondary sides. Only slight compositional differences were observed among green and yellow glazes. Some of these differences were due to elements responsible of the color of glazes. Although the final color of glazes was also influenced by the body color and the metallic oxide added into the glaze [12,14,17], the latter was the responsible of the compositional differences. Therefore, yellow/honey glazes had higher amounts of FeO (1.6–4% in yellow glazes, versus 0.6–1.7% in green glazes) and green coatings were richer in CuO proportions (1.2–4% in green glazes).


*s (n = 19) 0.24 0.29 0.72 1.4 0.46 1.44 0.74 3.7* green *mean* 0.94 0.74 4.53 40.4 2.84 3.98 1.17 2.56 1.80 41.0 *s (n = 17) 0.36 0.21 0.79 3.5 0.78 1.05 0.35 0.85 1.71 4.5*

**Table 4.** Chemical composition (%wt) of monochrome glazes by EDS.

An important feature of these monochrome glazes was the fact that all green glazes included tin oxide in their composition (Table 4). Tin was detected with EDS analysis and tin-oxide crystals were observed in the green glazes. Although the tin-oxide percentages were lower than white tin-opacified glazes (Table 3), the proportion was enough to give a certain opacity. This characteristic was also highlighted in green glazes from Zaragoza *Taifa* [22].

Inclusions were occasional in the main monochrome glazes (Figure 5), but they were always present in the secondary sides, which implied careful treatment of raw materials again, especially for the main sides. These inclusions were mainly quartz and feldspars. It is not easy to establish an average size of the inclusions because there was a lot of variation even inside the same specimen. The glaze thickness was quite constant in the same sample, but it varied significantly among different ceramic fragments. Additionally, not only the yellow/honey glazes but also the green glazes were thicker in the main side (100–150 μm for the yellow glazes, and 150–200 μm for the green glazes) than in the less important side (80–100 μm in the yellow glazes, and 100–150 μm in the green ones).

**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.

In these types of glazes, greater interactions between body and glaze were observed by SEM (Figure 5a). Since the reaction between ceramic paste and glaze was related with the type of developed firing process [12,17,21], it can be assumed that the thickness of the interface (35–40 μm) in monochrome glazes corresponded to a single firing process. This technique of manufacture justified the great amount of lead-potassium feldspar crystals that existed in the interface, and that favored the adhesion between both layers [23]. In addition, this type of firing process enhanced the diffusion of certain elements (such as aluminum and iron) from the body to the glaze. Aluminum and iron were incorporated into the glaze and helped the stabilization of PbO-SiO2 glazes. Therefore, the presence of aluminum and iron in the glazes can be attributed, on the one hand, to the raw materials of the glazes and, on the other hand, to the diffusion of components from the clay to the glaze during the firing process [12,17].

It can be pointed out that the composition of transparent yellow/honey glazes (Table 4) was very similar to that of the glazes employed on the secondary side of white glazes, especially to subgroup 1 (Table 3). Inclusions were abundant in both secondary-side glazes of yellow-honey glazed and white glazed ceramics.

The comparison of chemical compositions of the honey/yellow glazes from Albarracin with productions from other Islamic workshops [4,12,16,22] confirmed differences in lead/silicon ratios. Almost all productions whose workshops were situated in the south and SE part of the Iberian Peninsula had lead oxide content between 45–60% PbO. Lead percentages of glazes produced in Albarracin were among the lowest compared with the rest of the workshops. However, productions from Albarracin and Zaragoza *Taifas* had in common that their ceramics were manufactured with a unique firing process, whereas the rest of the centers of production seemed to prepare monochrome glazes on biscuited ceramics.
