Blue, one of the seven primary colors. Like the green of the forest and the field, nature appears to have adopted the color for the sea and sky with reference to its soft and pleasing effect upon the eye. In these, its various shades are seen in their highest perfection, and they are also most brilliantly displayed in the sapphire and the turquoise. In the arts, it is derived for dyes from the products of the vegetable, animal, and mineral kingdoms. Indigo is the most common vegetable material for producing it. A great variety of berries are also used, the juices of which become blue by the addition of alkali or salts of copper. Among mineral substances, cobalt is the most remarkable for the brilliant blue produced by its salts. Cobalt blue is used for coloring glass and porcelain. Mountain blue is derived from carbonate of copper. Bremen blue or verditer is a greenish blue color, obtained from copper mixed with carbonate of lime. Prussian blue, used for chemical purposes and as a pigment, is obtained from horns, hoofs, or dried blood; other blues are obtained from combinations of molvbdenum and oxide of tin.
Ultramarine is a beautiful blue pigment prepared from the mineral lapis lazuli, which until recently has defied all imitation.