I understand the basics of Allomancy and Feruchemy, but I'm unsure of how exactly the powers support each other so well. Namely: where does the EXTRA investiture come from when Compounding? How is it provided? And why do you get so much extra investiture?

Note: the question How does Compounding work? is focused on the mechanics - what do you have to do to "compound" your ability. While it notes that the end result is that the compounder winds up with more power than what they put into the system, it doesn't really address where that power comes from.

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    I don't see how this is a duplicate. Although the title of the question was "How does compounding work?" the body of the marked duplicate is not asking in reference to the source of power, so nothing in that question would really explain it. The other question is basically asking what a compounder physically does; but doesn't seem concerned about the aspect of it that this question is explicitly looking for.
    – JMac
    Jan 10 '19 at 17:26
  • Mm, I'm mainly confused on the subject of where the huge colossal inexplicable boost of power comes from when compounding is used. Two balanced systems being used together to gain unbalanced strength. As kindly explained, the power comes from Preservation, and is a result of the end positive nature of Preservations magic system. I did read "how does compounding work" before asking this question.
    – Isaac
    Jan 11 '19 at 15:07
  • Yeah, I had actually looked through several questions before I answered because I expected this to be a duplicate. When reading that question I noticed that the body of the question was focused on something completely different, and there was nothing about the power source. I couldn't find anything on this site that addresses this; it seems like people closed based on the title, not content.
    – JMac
    Jan 11 '19 at 15:11

Simple answer: extra investiture for compounding comes from Preservation.

Long answer: The mechanics of that are a little more complicated; but it's not too hard to understand once you understand the differences in the systems. With the metallic arts, you can classify the three systems as end-positive, end-neutral, or end-negative (source).

Allomancy is end-positive - the power for allomancy doesn't come from the person/metal. The metals just act as a key to Preservation's power. End-positive references that the use of allomancy basically adds Preservation's investiture into the physical realm from the spiritual.

Feruochemy is end-neutral - the power for feurochemy comes from the feruchemist themselves. No additional investiture is added to the physical realm, it is just stored in the metal without gaining or losing charge.

Hemalurgy is end-negative - when making a hemalurgic spike, the power that you steal is diminished compared to the person it is stolen from. Some of the investiture is lost from the physical realm. This fits with Ruin's want for things to decay.

So understanding all this, we can fairly easily explain how compounding works. With feruchemy, you are only able to store the investiture you have access to; it doesn't provide any key to a shard's investiture. Allomancy does provide a key to Preservation's investiture though. When a twinborn burns a metalmind with a feruchemical charge; they are able to key Preservation's power to that charge, and use their feruchemical abilities to store that additional power in a metalmind. They are able to convert the end-positive energy from allomancy with the end-neutral nature of feruchemy. This allows them to amplify feruchemical abilities, AKA Compounding.

See also this explaination from Brandon Sanderson (emphasis mine):

Lyndsey Luther: Ok, last question. It was really difficult coming up with three questions that haven’t been asked already...

Brandon Sanderson: OK... you’re not going to ask me the “what would you ask me” question?

Lyndsey Luther: Not quite...

Brandon Sanderson: OK good, because I hate that one! (laughs)

Lyndsey Luther: My question is if there’s anything that you’ve never been asked that you would like to talk about?

Brandon Sanderson: Oooooh, ok. Hm. That one is so hard! Every time people ask me something like this... What have I never been asked that people should be asking, is basically what the question is? Something that the fans have just missed... They pick up on so much, that it’s hard... I do wonder if, you know… all the magic systems [in my books] are connected and work on some basic fundamental principles, and a lot of people haven’t been asking questions about this. One thing I did get a question on today, and I’ll just talk about this one... they didn’t ask the right question, but I nudged them the right way, is understanding that tie between Aondor [the magic system from Elantris] and allomancy [Mistborn’s magic system].

People ask about getting the power from metals and things, but that’s not actually how it works. The power’s not coming from metal. I talked a little about this before, but you are drawing power from some source, and the metal is actually just a gateway. It’s actually the molecular structure of the metal… what’s going on there, the pattern, the resonance of that metal works in the same way as an Aon does in Elantris. It filters the power. So it is just a sign of “this is what power this energy is going to be shaped into and give you.” When you understand that, compounding [in Alloy of Law] makes much more sense.

Compounding is where you are able to kind of draw in more power than you should with feruchemy. What’s going on there is you’re actually charging a piece of metal, and then you are burning that metal as a feruchemical charge. What is happening is that the feruchemical charge overwrites the allomantic charge, and so you actually fuel feruchemy with allomancy, is what you are doing. Then if you just get out another piece of metal and store it in, since you’re not drawing the power from yourself, you’re cheating the system, you’re short-circuiting the system a little bit. So you can actually use the power that usually fuels allomancy, to fuel feruchemy, which you can then store in a metalmind, and basically build up these huge reservoirs of it. So what’s going on there is… imagine there’s like, an imprint, a wavelength, so to speak. A beat for an allomantic thing, that when you burn a metal, it says “ok, this is what power we give.” When it’s got that charge, it changes that beat and says, “now we get this power.” And you access a set of feruchemical power. That’s why compounding is so powerful.


  • the correct spelling should be feruchemy, my apologies for correcting it badly in my edit
    – fbstj
    Jan 16 '19 at 16:07

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