Blue overseas

The blue overseas or overseas is a pigment whose base is a thiosulfate of aluminosilicate of sodium. It was developed at the beginning of the XIXe century when European industry sought to be freed from the importation of indigo from the Indies. Nicholas Clement and Charles Desormes, by chemical analysis, had shown as of 1806 that the aluminosilicates used naturally the composition of the natural Lapis-lazuli.

The industrialists sought to synthesize this chemical compound starting from the clay, which also contains aluminosilicates. Conclusive results were obtained independently and almost simultaneously by the German chemist Christian Gottlob Gmelin (1824) and the French industrialist Jean-Baptiste Guimet (1826). The technique consists in heating to several hundreds of degrees a mixture of clay, caustic soda (for the sodium contribution) and of coal.

Nicholas Clément industrialized itself the Guimet process in its factory of Verberie.

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