Indigo, or Indian blue, is a pigment manufactured in the East and "West Indies from several plants, but principally from the Anil, or Indigofera. It is of various qualities, and has been long known and of great use in dyeing.
In painting it is not so bright as Prussian blue, but is extremely powerful and transparent, hence it may be substituted for some of the uses of Prussian blue, as the latter now is for indigo.
It is of great body and works well both in water and oil. Its relative permanence as a dye has obtained it a false character of extreme durability in painting, a quality in which it is very inferior even to Prussian blue.
Fig. 15. Roofing Brush.
Indigo is injured by impure air, and, in glazing, some specimens are firmer than others, but not durable, in tint with white lead they are all fugitive; when used, however, in considerable body in shadow it is more permanent, but in all respects inferior to Prussian blue in painting. Intense blue is indigo refined by solution and precipitation, in which state it is equal in color to Antwerp blue. By this process indigo becomes more durable and much more powerful, transparent and deep. It washes and works admirably in water; in other respects it has the common properties of indigo.
