A metalmind is a piece of metal in which Feruchemists store attributes, such as strength or warmth, in order to store them up for later use.[1] The specific attribute stored depends on the type of metal, and exactly how much of that attribute can be stored is dependent on the volume and purity of the metal. A metalmind may be ingested or even embedded in the skin as well as the more traditional method of simply wearing the metal.
When discussing specific kinds of metalminds they are generally referred to by the metal they are made of, for example a "coppermind" is a copper metalmind used to store memories.
The stored attribute of a metalmind can only be accessed by the feruchemist who stored it. Should another feruchemist attempt to use the metalmind they will be able to sense the stored power but not use it. Similarly, an Allomancer who burns the metalmind will be unable to use the power unless they are also a feruchemist and were the one to store the attribute. If this Allomancer is to burn their metalmind the stored attribute would be more powerful than were they to tap the metalmind.
Filling a metalmind is the work of weeks; a steel bracelet, for example, can take up to 30 days of active storage to fill up.[2] Even filling a ring can take weeks.
There seems to be no limit to how many different attributes can be stored simultaneously, although filling more than a few at once is rare. The only downside seems to be quality of life.[3]
Some Feruchemists design their metalminds to have disconnecting gaps, so they'll bend as opposed to constrict in the change of size brought on by tapping pewter.[4]