Brandon Sanderson - Shadows of Self

In truth, this isn’t much different from the form-based Investitures one finds on Sel, where specific shape is the key—here, however, the interactions are more limited. Still, one cannot deny the raw power of Allomancy. It is instinctive and intuitive for the practitioner, as opposed to requiring a great deal of study and exactness, as one finds in the form-based Investitures of Sel.

Allomancy is brutal, raw, and powerful. There are sixteen base metals that work, though two others—named the “God Metals” locally—can be used in alloy to craft an entirely different set of sixteen each. As these God Metals are no longer commonly available, however, the other metals are not in wide use.

Feruchemyis still widely known and used at this point on Scadrial. Indeed, you might say that it is more present today than it has been in many eras past, when it was confined to distant Terris or hidden from sight by the Keepers.

Feruchemy is an end-neutral art, meaning that power is neither gained nor lost. The art also requires metal as a focus, but instead of being consumed, the metal acts as a medium by which abilities within the practitioner are shuttled through time. Invest that metal on one day, withdraw the power on another day. It is a well-rounded art, with some feelers in the Physical, some in the Cognitive, and even some in the Spiritual. The last powers are under heavy experimentation by the Terris community, and aren’t spoken of to outsiders.

It should be noted that the inbreeding of the Feruchemists with the general population has diluted the power in some ways. It is now common for people to be born with access to only one of the sixteen Feruchemical abilities. It is hypothesized that if one could make metalminds out of alloys with the God Metals, other abilities could be discovered.

Hemalurgyis widely unknown in the modern world of Scadrial. Its secrets were kept close by those who survived their world’s rebirth, and the only known practitioners of it now are the kandra, who (for the most part) serve Harmony.

Hemalurgy is an end-negative art. Some power is lost in the practice of it. Though many through history have maligned it as an “evil” art, none of the Investitures are actually evil. At its core, Hemalurgy deals with removing abilities—or attributes—from one person and bestowing them on another. It is primarily concerned with things of the Spiritual Realm, and is of the greatest interest to me. If one of these three arts is of great interest to the cosmere, it is this one. I think there are great possibilities for its use.

It is possible on Scadrial to be born with ability to access both Allomancy and Feruchemy. This has been of specific interest to me lately, as the mixing of different types of Investiture has curious effects. One needs look only at what has happened on Roshar to find this manifested—two powers, combined, often have an almost chemical reaction. Instead of getting out exactly what you put in, you get something new.

On Scadrial, someone with one Allomantic power and one Feruchemical power is called “Twinborn.” The effects here are more subtle than they are when mixing Surges on Roshar, but I am convinced that each unique combination also creates something distinctive. Not just two powers, you could say, but two powers … and an effect. This demands further study.