NBr11

Bistre is rare as a pigment, where it was used in watercolor to make soft brown washes. It had a variety of sources, and is basically a soot from Birch trees (Betula genus).

According to CAMEO, it was "…Prepared by boiling the tarry soot of burnt resinous woods in water, then mixing in Gum arabic and drying to form a cake. Beech trees were the preferred wood, but Pine and Willow were also used."

Kremer pigments writes, "Bistre may have been superior to asphaltum as a water color, although it was not altogether easy to use, its slightly resinous character making it difficult to work with and mix with other colors. Spanish liquorice was often incorporated with it to improve its working properties and impart a richer tone, but such an addition was detrimental because liquorice brown was fugitive."

Sasha Duerr's book Natural Palettes mentions that Birch naturally sheds its bark, so it can easily be picked up around the forest and there is no need to harm the tree by harvesting it directly. As a dye, birch bark can also be used to create pinks and purples.

Oddly, for NBr11, see also Mummy brown. CAMEO lists mummy brown as NBr11.