13 ноября, 2015 
Pokraskin The naturally occurring mineral lapis lazuli is found in very few places around the world with the best quality being obtained from Afghanistan and Chile. The name “Ultramarine” meaning from “across the sea” was given to the pigment derived from grinding the mineral. The deep blue color was used by many artists and can be seen in Giotto’s chapel in Padua, on Duccio’s Virgin and Child and on Renoir’s La Parapluie amongst others. The cost of transport of the mineral and subsequent processing meant that the pigment was more expensive than gold. As a result, the French Government launched a competition in the 1820s, with the prize being given to the first synthetic and economic process to make ultramarine blue.
The result of the competition is shrouded in controversy, but the common view is that Guimet in France and Gmelin in Germany independently devised similar processes for synthetic preparation in 1828 [3.153]. The prize was awarded to Guimet and he is frequently referred to as the first person to produce ultramarine blue on a commercial scale.
Synthetic ultramarines are inorganic powder pigments, commercially available in three colors:
1. Reddish blue, C. I. Pigment Blue 29: 77007 [57455-37-5]
2. Violet, C. I. Pigment Violet 15: 77007 [12769-96-9]
3. Pink, C. I. Pigment Red 259: 77007 [12769-96-9]
The proportions of the chemical constituents can vary, but the typical lattice repeat unit of a blue ultramarine is Na6.9Al5.6Si6.4O24S42. The violet and pink variants differ from the blue mainly in the oxidation state of the sulfur groups. This is reflected in somewhat lower sodium and sulfur contents.
3.5.1
Опубликовано в рубрике 