cobalt blue decoration

Ingredients

cobalt, lead, tin

Preparation Steps

Original Recipe Text

The process began with the shaping of the bowl, often using a wheel and then inverting it over a convex (drape) mold to define the interior shape and allow for exterior trimming. (p. 4) The yellow clay body was then covered with an opaque white glaze composed of lead as a major constituent and tin as an opacifier to mimic Chinese porcelain. (p. 4) Cobalt blue decoration was then added over this white surface to create the 'ink on snow' effect. (p. 6) The entire vessel was fired at high temperatures of nearly 1000 degrees Celsius, which was 200 degrees Celsius higher than traditional Mesopotamian firing temperatures. (p. 5)

Evidence

"analysis of these early glazes using the new X-ray fluorescence (XRF) spectrometer at the Freer shows that a glaze recipe combining tin and lead was not transmitted intact, and that considerable experimentation occurred in Basra."

Remarks

Early Islamic blue-and-white wares from the first half of the ninth century have been found from Aqaba to Quanzhou. (p. 1) Analysis at the Smithsonian Institution revealed that the opaque white glaze on these wares shows significant compositional variation, suggesting that the Basran potters were experimenting with recipes to achieve the desired whiteness and opacity. (p. 5) These Islamic wares are believed to have inspired Chinese potters to experiment with blue-and-white combinations in the 14th century. (p. 6)