Cobre
Copper is the internal mental pulling metal. An Allomancer burning copper is able to hide Allomanctic pulses emanating from those around him, and is immune to emotional Allomancy. Feruchemists can use copper to store memories, and when used as a Hemalurgic spike, copper steals mental fortitude.
Allomantic Use
A copper Misting is known as a Coppercloud or Smoker. Other Allomancers near a Smoker are protected from Seekers (bronze Allomancers).[1] With the exception of Seekers pierced by bronze Hemalurgic spikes from another Seeker, it is impossible to sense Allomancy being used inside the cloud. Smokers are of central importance when Allomancers are trying to hide.
An important side effect of burning copper is that the Smoker himself is protected from emotional Allomancy. There is some contention on if this holds for other people in the cloud.[2]
Feruchemical Use
A copper Ferring is known as an Archivist. Copper is used to store memories.[3] This ability forms the core of the Keepers, a group of Terrismen dedicated to preserving knowledge. Since the memories in a coppermind do not degrade with time (although they are vulnerable to Ruin's manipulation), it is perfect for the collection of enormous quantities of facts. For this reason, Feruchemists were much more likely to be scholars than warriors. When a Feruchemist stores a memory in a metalmind, it immediately disappears from his memory. The best users of copperminds would create indexes to find memories much faster. Finally, the longer a memory sits outside of a coppermind, the more it degrades.[4]
Hemalurgic Use
When used as a Hemalurgic spike, copper steals mental fortitude.