0 a reddish-brown colour
A clay of limonite rich in iron oxide is the source of raw sienna and burnt sienna.
When heated, it becomes a reddish brown and is called burnt sienna.
From volume 25 (1964) onwards, all volumes have been published in a uniform burnt sienna hardback binding.
The embryonic whorls are burnt sienna brown (weathering to whitish in adult shells), or sometimes there is a light median zone.
