Bitumen
The pigment that destroyed the paintings it was used in. Bitumen gives a deep, glowing, transparent brown unlike anything else, and it never dries — decades later it is still moving, and the surface above it tears itself apart.
Origin
Bitumen is naturally occurring asphalt, seeping from the ground in Trinidad, in the Dead Sea region and elsewhere, and it entered the palette as a cheap source of transparent darkness in the seventeenth century. Its notorious variant, mummy brown, was made by grinding actual Egyptian mummies — bitumen-impregnated human and animal remains — and was sold by European colourmen from the sixteenth century into the twentieth. The trade was real, well documented and entirely matter-of-fact in the catalogues; the artist Edward Burne-Jones is reported to have buried his tube in the garden on learning what was in it. Supplies ran out not from scruple but from scarcity.
In art history
Bitumen belongs above all to the late eighteenth and early nineteenth centuries, when a taste for warm Old Master darkness collided with a poor understanding of materials. It appears in five eras here. Reynolds used it and much of his work has suffered accordingly; Delacroix and the French Romantics used it; Géricault's Raft of the Medusa is the most cited casualty, its darks now a wrecked, deeply fissured surface that no longer reads as the painter intended. The appeal is understandable: nothing else gives that particular smoky transparent depth, and it looks magnificent for about twenty years.
In the studio
The problem is that bitumen is not a pigment at all — it has no crystalline particles, it is a soft hydrocarbon that dissolves into the oil rather than dispersing through it. So it never forms a solid film. It stays permanently soft and slowly flows, and the paint layers above it, which have hardened normally, crack into the wide, deep, alligator-skin pattern that is the unmistakable signature of bitumen use. It also bleeds upward through subsequent layers, browning them. There is no remedy; conservation can stabilise the surface but cannot reverse it, and a bitumen picture continues to deteriorate.
Afterlife
Its failings were understood by the mid-nineteenth century and it was gradually abandoned, though warnings took decades to displace the habit. Nothing replaced it exactly, because nothing else had its optical quality; painters wanting transparent dark now use burnt umber, transparent oxide brown or a mixture of ultramarine and burnt sienna. Mummy brown was still listed by at least one London colourman until 1964, when the firm announced it had run out of mummies.
Where it appears
Every era and artist in this atlas whose palette includes this pigment.