Shades of turquoise and deep blue sing out on ceramics made in the Islamic world. Generations of potters throughout the region have shared the distinctive mineral colors of cobalt blue and copper green, using them as pigments to write and paint on clay or as colorants to saturate glazes. The vessels on view in Sky Blue: Color in Ceramics of the Islamic World, opening tomorrow, were created in Iran, Iraq, Syria, and Uzbekistan, and span the ninth through the nineteenth century.
Over the centuries, potters have perfected a complex process to incorporate these colorants into their glazes. In Iran, for example, potters ground quartz pebbles into a fine powder to provide the silica (the “glass”) needed in traditional glaze-making practices. The ash of burned plants was a source of alkali fluxes that helped the silica melt. Silica and ash were usually combined and heated to produce a glass that was then shattered and ground into frit. This was mixed with water and other ingredients to make a glaze. Cobalt or copper oxide was added for color.
Typically ceramic vessels were first fired without glaze to harden the body. They were then coated with glaze and fired again at a temperature high enough to melt the frit mixture into a smooth, translucent surface. Lead and tin oxides were added if an opaque glaze was desired. Sometimes vessels were fired several times, depending on the complexity of the decoration.
The cheerful, eye-catching shades of blue and green belie the effort required to bring them forth. Abdul Matin Malekzadah, a potter from Afghanistan whose work is on view in the exhibition Turquoise Mountain, describes the blue-green glaze of his bowls as “the color of peace, the color of competence.”