Hidden in the Glaze: Cobalt Blue Decorations of Catalan Tin‐Glazed Ceramics From the 16th to 18th Centuries

This study investigates technological evolution in 16th–18th century Catalan tin glazes and cobalt blue decorations. Analysis reveals three glaze strategies, highlighting shifts in tin oxide use and cobalt pigment composition. In the 16th century, tin oxide acted as an opacifier and cobalt pigments exhibit low arsenic content with CoO/NiO and CoO/FeO ratios around 1.2. The 17th century shows residual tin and increasing manganese in pigments, while the 18th‐century glazes reintroduce tin with a Co–Ni–Fe–Mn glassy pigment (CoO/MnO ≈ 0.85). Nanometric arsenate particles within glazes produce diffuse brown halos in thin sections, offering a novel microstructural marker for archaeometric studies.