Burnt Sienna: Natural calcined (roasted) earth pigment. More opaque today than 200 years ago because large industrial users of earth colors prefer more opaque pigments. Remember no pigments are made just for artists. We borrow from all other industries. For greater transparency, consider Gamblin Transparent Earth Colors and Van Dyke Brown. Pigment: Calcined natural iron oxide (PBr 7) Vehicle: Alkali refined linseed oil Lightfastness I, SEMI-TRANSPARENT.