Burnt Sienna

The roasting or calcination of raw sienna produces a very great change in its hue as well as in the depth of its colour. The ferric hydrate of the raw earth becomes wholly converted into ferric oxide, this change being accompanied by a great increase in the translucency and depth of the colour.

When small fragments (or the coarse powder) of raw sienna are calcined, it will be noticed that the change of hue which occurs is not quite uniform, some points being of a brighter and redder brown than others. A very fine powder, thoroughly stirred during roasting, shows this peculiarity in a much less marked degree.

Burnt sienna possesses a very beautiful, warm, reddish-brown hue, which cannot be exactly imitated in translucency and depth by mixtures of other pigments. It is permanent, without action on other pigments, and not liable to adulteration. It is available for use in every method of painting. Some fine and permanent foliage-greens may be made by associating viridian with burnt sienna.