Coal.
Raw petroleum; crude oil.
Black pepper, in the context of being a historically valuable spice.
Black-coloured gold, variously produced by patination, deposition, oxidation, etc. and used in jewellery or in high-technology applications.
A sediment of accumulated minerals in a steam boiler.
A residual semi-solid material left from industrial, water treatment, or wastewater treatment processes.
Solids separated from suspension in a liquid.
A mass of small pieces of ice on the surface of a body of water.
sludge metal
To slop or drip slowly.
To slump or slouch.