Thaolet

Thaolet was an oil made by dwarves and used for protecting metals from moisture. It was also used to remove rust and tarnish from metal surfaces and blood from weapons.

Description
Thaolet was made by boiling certain plants and then mixing the result with the dust of particular types of stone. This created a black grimy oil that had preservative properties against moisture and oxidation. It was typically used to cleanse and preserve armor. Often a small barrel of thaolet was kept open near a workbench, anvil, or somewhere on a work site to submerge all but the handles of tools when not in use.

Thaolet was actually edible, but by all accounts it tasted terrible.