The colour we now call Raw Sienna was known in earlier times as Terra di Siena – the earth of Siena – because it was around Siena (Italy) that large deposits of this color were found. The deposits used since Roman times finally became depleted in the 1940’s and now the major sources of the pigment are in Sardinia, Sicily and in the eastern United States. It is browner than Yellow Oxide and matches the many brownish yellows found in nature. Its distinctive colour was formed over a long period of time with most of the deposits being from the Precambrian period, which ended 542 million year ago. Being a natural product this colour is represented by a range of color variation just as natural as Yellow Oxide is and the variation is so great that the two pigments overlap and it is an arguable point as to whether or not the brownest versions of Yellow Oxide should really be called Raw Sienna, and conversely whether the yellowest shades of Raw Sienna should really be called Yellow Oxide. It is this uncertainty, which is the reason why the Raw Sienna made by Matisse is officially designated as PY43 – which is the color index name for natural Yellow Oxide.
Chemical Description: Natural iron oxide
Pigment Number: PY43
Lightfastness Rating: ASTM I
Pigment Opacity: Transparent
Paint Opacity: Semi-Transparent