Flux (glass melt)

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Flux (glass melting) are needed to the melting temperatures of in the glass production quicklime (2500 ° C) and silica sand (1700-2000 ° C) to reduce to around 1450 ° C, the normal operating temperature in the glass furnace, and thus energy to save up. Potassium carbonate ( potash ) was used for this until the 18th century . Since then, industrially produced, comparatively cheap sodium carbonate ( soda ) has been used. Its melting point is 853 ° C.

For high-quality, pure white crystal and lead crystal glass, potash with a melting point of 884 ° C is still used in some cases, with potash usually being made from potassium hydroxide . In antiquity and in the Middle Ages it was made from the ashes of salt plants ("potash glass"), later from beech wood ("forest glass"), whereby the ashes were soaked in vats and leached in several steps. The lye was then evaporated in brewing kettles and the residue was burned to give white-calcined potash. To produce 1 kilogram of potash, 2 stars of wood were required, so that beech wood became scarce even in wooded areas of Europe.

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