Burnt Siennas and Red Earth Pigments
Burnt Siennas and Red Earth belong to a category of earth tones that are similar to Ochres but extend into deep rich shades of orange and red. All of these are considered by many artist as pigments "they cannot live without". These are common ores which occur throughout the world and new ones are constantly being discovered.
Red Earth is a naturally occurring ore rich in iron oxide. It's commonly classified as Ferric Iron Oxide. The difference between Red Earths and Siennas is in the amount of iron and silica as well as the conditions it was exposed to greatly influencing it's transparency. Venetian Red is a type of Ferric Iron Oxide.
Burnt Sienna starts out as Raw Sienna but is turned red by calcination. As with Raw Sienna the color range of Burnt Sienna can range from bright warm orange to red-brown. The iron content of Burnt Sienna can greatly influence it opacity. The higher the iron content the stronger the tinting strength as well as it opacity.