Sienna

#A0522DFormula Fe₂O₃·nH₂OEarliest recorded use Prehistoric

20 eras38 artists48 colors

The transparent earth. Sienna sits between ochre and umber, and what distinguishes it is not its colour but its clarity: it is the only iron oxide that glazes properly, and that single property gave it a permanent place on the palette.

Origin

Named for Siena in Tuscany, where the best deposits were worked from the Renaissance onwards, sienna is a hydrated iron oxide with a small amount of manganese — less than umber, more than ochre — and a fine, silica-rich clay that makes it unusually translucent. Raw sienna is a warm brownish yellow. Burnt sienna, roasted like every other earth, is a deep reddish orange-brown, and is the more used of the two by a considerable margin. The Tuscan mines are largely exhausted; most sienna sold today comes from elsewhere or is synthetic, which is why older painters sometimes complain that modern burnt sienna is not what it was.

In art history

Sienna is a workhorse without a manifesto — it turns up in fourteen eras of this atlas without ever being the point of a painting. Its historic role is flesh. Mixed with white it gives a convincing mid-tone for skin across a wide range of complexions, and glazed thin over a lighter underpainting it produces the warm translucency that flesh actually has, because human skin is itself a translucent layer over something lighter. The Venetians understood this and built their flesh painting on exactly that logic. It is also the standard warm dark in watercolour, where its transparency makes it indispensable, and it is the colour of a great deal of nineteenth-century landscape foreground.

In the studio

Transparency is the whole story. Opaque earths sit on the surface; sienna lets light pass through it and bounce back off whatever is underneath, which is why a burnt sienna glaze over white is luminous in a way that burnt sienna mixed with white is not. It is completely lightfast and inert, compatible with everything, and dries at a moderate to fast rate in oil thanks to its manganese. In watercolour it granulates attractively, settling into the texture of the paper. The one caution is the same as with umber: it dries faster than most colours, so it should not go underneath slower layers.

Afterlife

Still universally available, though genuine Tuscan sienna is largely a thing of the past and most tubes now contain synthetic iron oxide adjusted to the traditional hue. The synthetic version is stronger and more consistent but tends to be more opaque, which loses precisely the quality that made the natural earth worth having.