Bas-Lag Wiki

Rockmilk is a thaumaturgical substance that is found deep under the surface of Bas-Lag, with the ability to greatly supercharge thaumaturgy. New Crobuzon is one of the few city-states that can extract rockmilk from deep under the seabed.


Rockmilk is pure white and bone-cold to the touch, distinct from hydrocarbons like petroleum.


As with conventional fetishes and chymicals, rockmilk can be used as a thaumaturgical aid, albeit one with much greater effectiveness. In 1780, the floating city-state of Armada used a captured New Crobuzon rig, the Sorghum, to extract vast quantities of rockmilk for using in summoning an avanc.