Ultramarine artificial
Composition and Properties of Ultramarine Artificial
Ultramarine is a complex sodium silicate containing sulfur and aluminum with the chemical formula Na7Al6Si6O24S3. The intense and unique blue color is caused by the unpaired electron in the sulfur radical anions S3-.It is chemically stable under normal conditions and is also resistant to high temperatures as well as to alkaline solutions and can thus be employed in fresco. It is, however, unstable even in dilute acids and decomposes to yield hydrogen sulfide.There are no known incompatibilities with other pigments.
Names of Ultramarine Artificial
French ultramarinePB 29, CI 77007From Medieval Latin ultramarinus, literally “beyond the sea,” from ultra– “beyond” + marinus “of the sea”. Said to be so called because the mineral was imported from Asia.From WordFinde
Preparation of Ultramarine Artificial
A number of historical recipes for the preparation of artificial ultramarine have been investigated recently by Hamerton, Tedaldi, and Eastaugh who compared the colour of the product prepared by the different methods (1). They found that the optimum method for preparing artificial ultramarine is heating a homogenized, pelletized mixture of kaolin (100 parts), sodium carbonate (100 parts), bitumen emulsion (or any ‘sticky’ carbon source) (12 parts) and sulfur (60 parts) at 750°C for ca. 4 hours.
History of Use
After the successful synthesis of artificial ultramarine in 1828, the exceedingly expensive natural ultramarine was rapidly substituted by the cheaper artificial product. It has been used extensively by the Impressionists and Post-Impressionists. The following graph gives the frequency of its use in the paintings of the Schack Collection in the Bavarian State Art Collections in Munich (1).References(1) Kühn, H., Die Pigmente in den Gemälden der Schack-Galerie, in: Bayerische Staatsgemäldesammlungen (Ed.) Schack-Galerie (Gemäldekataloge Bd. II), München 1969.Example of use
