![]() That did not remain true for long, however. ‘Oxide of cobalt forms a green color when heated with oxide of zinc but as this compound is expensive, it is not in use,’ Overman pointed out in his book. It was also used as a pigment to make Chinese blue and white porcelain from the 13 th century onwards.Ĭobalt oxide was not used just to make blue pigments. The use of smalt on ceramics can be traced back much further – to about 1500 BC when it was used as a blue glaze for Egyptian pottery. ![]() Chemistry students may recall using cobalt blue glass in flame tests to filter out the bright yellow light of the sodium flame. Harveys Bristol Cream sherry, for example, has been sold in distinctive Bristol blue glass bottles since the 1990s. By the 1780s they were manufacturing high-quality glassware stained blue using Cookworthy’s imported smalt.īristol blue glass, as it became known, soon became popular and can still be seen today in stained glass windows and a variety of commercial products. In 1774, Lazurus, an expert glass cutter, and the 17 year old Isaac established a firm to manufacture glass products. Lazarus was born in Frankfurt, Germany, in 1709 and emigrated to Bristol around 1760. One of the most famous glass making firms was run by father and son team Lazurus and Isaac Jacobs. Much of the glass was exported to the American colonies. It gave an attractive blue glaze to the white porcelain his factories produced.Īt the time, Bristol was renowned for glass making, notably bottle and window glass. Over the following 20 years or so, he shipped the material to Bristol. In 1753, William Cookworthy, an enterprising English pharmacist and porcelain manufacturer, acquired exclusive rights to the smalt produced at the Royal Saxon Cobalt Works in Schneeberg, a town in Saxony. The cobalt ores ‘occur frequently so blended with ores of silver, that as one or the other metal must be sacrificed, it is often a matter of calculation to which works it will be most advantageous to deliver them.’ So said Welsh industrialist John Vivian at a meeting of the Royal Geological Society of Cornwall in February 1814.Įven so, during the 18 th and 19 th centuries the manufacture and marketing of smalt prospered in Saxony. The quality and value of the ores varied immensely, however. ![]() Mining ores containing metals such as cobalt had taken place in the region for centuries. Overman spent part of his career working at an engineering establishment in Chemnitz, a city in the German state of Saxony that is surrounded by the Ore Mountains.
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