Burnt Sienna is considered one of the most essential colours of the artist palette, one of the earth quartet colours. It was a standard colour on the palettes of Carravaggio and Rembrandt. Burnt Sienna contains a large amount of iron oxide, which helps to sped the drying properties. It is made by heating raw sienna, which dehydrates the iron oxide, changing it partially to haematite, giving it rich reddish brown colour. Paint makers who use large mills to make this colour must cool their mills with water, because the pigment can actually change color during processing. Raw Sienna has even more problems in this area. It is a great colour that has been made by hand for centuries.
Burnt Sienna is also known as red earth, red ochre, and terra ros. It is not considered toxic. CI:Pr102
ASTM I - Excellent