A yellow-brown colour, sienna is part of a group collectively known as earth colours*. Shades of sienna vary in hue and have different names depending on the colour. Raw sienna comes from iron ore or ferric oxide found naturally in clays. Unlike yellow ochres, which are generally opaque, siennas are more transparent.
Sienna was one of the first pigments used for painting and can be found in prehistoric cave art. But it was not until the dawning of the Renaissance in the 14th century that the pigment was further developed for artistic use. It takes its name from the place it was produced, the Italian city-state of Siena. During this time the Italians enhanced the range of hues for the pigment by roasting sienna, leading to the creation of raw sienna and burnt sienna pigments. These earth colours featured heavily in Renaissance painting techniques.
As the Tuscan deposits of raw sienna became depleted, Italian siennas increasingly came from other locations, such as Sicily and Sardinia. Small quantities of sienna have also been mined in Germany’s Harz Mountains. These alternative ores were not always of the same quality, leading colourmen to look to synthetic pigments.
Until 1988, Winsor & Newton bought sienna pigments with a beautiful bright undertone from a mine south of Siena. When the mine was closed, we bought the remaining stocks, which lasted until 1991. After this, there were no potential suppliers of siennas with the same bright undertone. But transparent synthetic iron oxides had already been on the market for some time, and these were evaluated and found to have the same transparent undertone, closely matching old standards, and are used today.
*Earth colours is a collective term given to naturally occurring colours which come from the earth, for example iron oxides from clay. They include yellow ochre, raw sienna, burnt sienna, raw umber, burnt umber and terre verte.