Sienna is an earth pigment containing iron oxide and manganese oxide. In its natural state, it is yellowish brown, and it is called raw sienna. When heated, it becomes a reddish brown, and it is called burnt sienna. It takes its name from the city-state of Siena, where it was produced during the Renaissance. Along with ochre and umber, it was one of the first pigments to be used by humans, and is found in many cave paintings. Since the Renaissance, it has been one of the brown pigments most widely used by artists.
The clay soil of Tuscany (here near Monteriggioni) is rich in limonite, or hydrated iron oxide, the main component of sienna pigment.
Limonite, a clay containing iron oxide, which gives sienna pigment its color.
Haematite. When roasted, limonite is converted partially to haematite and its colors turns more reddish.
After heating, the pigment becomes the color burnt sienna.
Ochre, iron ochre, or ocher in American English, is a natural clay earth pigment, a mixture of ferric oxide and varying amounts of clay and sand. It ranges in colour from yellow to deep orange or brown. It is also the name of the colours produced by this pigment, especially a light brownish-yellow. A variant of ochre containing a large amount of hematite, or dehydrated iron oxide, has a reddish tint known as red ochre.
Ochre pigment
Yellow ochre (Goldochre) pigment
Limonite, a mineraloid containing iron hydroxide, is the main ingredient of all the ochre pigments.
Hematite is a more reddish variety of iron oxide, and is the main ingredient of red ochre.
