Burnt Sienna (Liquitex Bio-Based Heavy Body)Bio Based Heavy Acrylic Burnt Sienna In Stock Now! Available sizes: 75ml (2. 5oz) 500ml (16. 9oz) A rich warm brown single pigment color made by burning raw sienna. Sienna is a natural yellow clay found in the earth and deepens in color when heated. It's one of the oldest pigments in its natural state and can be found in prehistoric cave art. Named after Siena in Italy, where the pigment was sourced during the Renaissance, it is a opaque color with