Note:  Do not rely on this information. It is very old.


Ultramarine. The well-known pigment of this name was formerly entirely obtained from the naturally-occurring mineral lapis-lazuli, and was then much prized and very costly. The observation, however, of blue masses in the furnaces used for the preparation of soda led to an artificial preparation of the compound, which was first effected by Gmelin 1828. It is now manufactured by heating a mixture of clay, glauber salt, white sand, sulphur, and resin, in crucibles placed in suitably-arranged furnaces. The exact constitution of ultramarine is unknown, and analyses of different samples vary. They all contain, as essential constituents, silica, alumina, soda, and sulphur, and may perhaps be regarded as a variable thiosilicate of alumina and soda. The varieties are usually more stable the more silica there is present. The pigment is very largely employed for the manufacture of water- and oil-colours, for paper-staining, and also in calico print.