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Cobalt glass for decoration. Cobalt glass—known as "smalt" when ground as a pigment—is a deep blue coloured glass prepared by including a cobalt compound, typically cobalt oxide or cobalt carbonate, in a glass melt. Cobalt is a very intense colouring agent and very little is required to show a noticeable amount of colour.
It is uncertain when Bristol blue glass was first made but the quality and beauty of the glass swiftly gained popularity, with seventeen glass houses being set up in the city. [3] Lazarus and Isaac Jacobs were the most famous makers of Bristol blue glass in the 1780s. Lazarus Jacobs was a Jewish immigrant to Bristol from Frankfurt am Main, Germany.
Blue glass was manufactured in Mesopotamia and Egypt as early as 2500 BC, using the same copper ingredients as Egyptian blue pigment. They also added cobalt, which produced a deeper blue, the same blue produced in the Middle Ages in the stained glass windows of the cathedrals of Saint-Denis and Chartres. [ 15 ]
Details of the process and the composition of the glass vary and so do the results, because it is not a simple matter to obtain or produce properly controlled specimens. [5] Small concentrations of cobalt (0.025 to 0.1%) yield blue glass. The best results are achieved when using glass containing potash. Very small amounts can be used for ...
Diluted light blue, though, is used to describe the color of fine-textured Egyptian blue that has a large amount of glass formed in its composition, which masks the blue color, and gives it a diluted appearance. It depends on the level of alkali added to the mixture, so with more alkali, more glass formed, and the more diluted the appearance. [13]
Low concentrations (0.025 to 0.1%) of cobalt oxide (CoO) produce rich, deep blue cobalt glass. [124] Chromium is a very powerful colouring agent, yielding dark green. [125] Sulphur combined with carbon and iron salts produces amber glass ranging from yellowish to almost black. [126]
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It was also used as colorant, particularly in blue glass and as the blue pigment used for centuries in Chinese blue and white porcelain, beginning in the late eighth or early ninth century. [15] Cobalt glass, or Smalt, is a variation of cobalt blue. It is made of ground blue potassium glass containing cobalt blue.
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