History
The earliest known example of cobalt aluminate glass dates to a lump from about 2000BC in ancient Mesopotamia, very possibly intended for use as a pigment; it is then rare until the modern era. About five centuries later cobalt oxide smalt appears as a pigment in Egyptian pottery, and soon after in the Aegean region, and this is the pigment normally known as smalt. In paintings, smalt has a tendency to lose its colour over a long period and is little used today. However used in ceramics for underglaze decoration it keeps its colour well, and is the main blue used in blue and white pottery from a wide range of dates and areas, including Chinese blue and white porcelain from the Yuan and Ming dynasties, Renaissance Italian maiolica and Delftware.
Chinese porcelain used smalt glazes from the Tang Dynasty onwards, though Chinese cobalt glass is found from the Chou dynasty (1122-221 BC). Cobalt was used as a pigment in Central Asia from the 13th century. A fragment of a mud painting in the ancient Tangut city of Khara-Khoto has been found to contain smalt, judged to be dated between 11th to 13th century. A large quantity of smalt was purchased for the decoration of the gallery of François Ier at Fontainebleau in 1536. Smalt, normally now discoloured, is common in European paintings from the 15th to 17th centuries. for example, it was found in Hans Holbein the Younger's portrait of Sir William Butts (ca. 1540), in Michael Pacher's painting "The Early Fathers' Altar" (ca. 1483), and in the frescos of Domenico Ghirlandaio (1449–1494).
The invention of a European smalt process is sometimes credited to a Bohemian glassmaker named Christoph Schurer, around 1540-1560 The process used for producing cobalt smalt glass at the Blaafarveværket industrial manufacturing center in Norway in the 19th century has been documented as smelting cobalt oxide together with quartz and potassium carbonate. The result was an intensive blue glass-like substance that was ground and sold to producers of glassware and porcelain.
Read more about this topic: Cobalt Glass
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