* Iron Oxide Pigments:
* Burnt Umber: This is a natural earth pigment containing iron oxides and manganese oxides. "Burnt" umber is umber that has been heated, which dehydrates the iron oxides and deepens the color to a warm, dark brown.
* Raw Umber: Similar to burnt umber, but not heated. It's a cooler, more muted dark brown.
* Brown Ochre: Contains iron oxides and clay, leading to a lighter, more yellow-brown shade compared to umber. Heating it can darken the color.
* Melanin: The pigment responsible for skin, hair, and eye color in animals. While not typically extracted for widespread pigment use, it's a natural dark brown (or black) pigment.
* Sepia: Derived from the ink sac of cuttlefish. It produces a rich, transparent brown. Less common now due to ethical and conservation concerns (synthetic versions are widely available).
* Catechu (Cutch): An extract from acacia trees. It yields brown dyes and pigments.
* Walnut Hulls: Extracts from walnut hulls can be used to create brown dyes and pigments.
* Charcoal: Produced by burning wood. Although often more gray or black, the shade can be a dark brown depending on the wood source and the burning process.
Important Considerations:
* Lightfastness: The resistance of a pigment to fading when exposed to light varies greatly. Some natural pigments, like iron oxides, are very lightfast. Others may fade over time.
* Toxicity: While generally safer than many synthetic pigments, it's important to research any pigment's potential toxicity and handle it appropriately.
* Transparency/Opacity: Some natural brown pigments, like Sepia, are transparent, while others like umber are more opaque.
* Availability and Cost: The availability and cost of these pigments vary.
In summary, burnt umber is probably the most widely used and readily available natural dark brown pigment. It is valued for its permanence, opacity, and relatively low cost. Iron oxides in general are reliable options. However, the best choice will depend on the specific application, desired shade, and desired properties of the pigment.