I love the thoughts you've given here, but I have to say I disagree with your 6 versions of compounding.
the reason is thus:
this limits the number of different kinds of compounding there can be, as well as limiting their utility. Why? because you cannot begin an Allomantic process without finishing it.
Beyond this one point, I would cite examples from the books, as well as a small amount of logic.
Above anything else, Brandons magic is simple, logical, and predictable. other wise we wouldn't get to debate it this way at all.
My edition of the 6 versions of compounding is thus:
1. Allomantically powering Feruchemy -> Store attribute, burn metalmind, gain powers!
- Gains Benefits of Extra Investiture
- Also consumes metalmind
- Must be a Twinborn for the same metal.
*This is all entirely correct. most of what we know of compounding comes from examples of this form. In many cases, it is also wise to store excess Ferrochemic power in a metalmind.
Example: Brandon has previously stated that compounding Atium can reduce an adult to infancy.
2. Feruchemically powering Allomancy -> Burn metal, somehow store power in a metalmind, tap to use.
*There are two basic possibilities for this:
*Store with Nicrosil: you may use this method with any allomantic metal. The advantages / possibilities of this are endless. The net result is similar to duralium use.
-Technically, a Nicrosil Ferring is able to store Investiture from any source he has access to. This allows a Twinborn to burn metals without them generating their normal effect. The investiture may then be stored for latter use.
-When tapping Nicrosil Ferrochemically, it will have a direct effect only if it is used in conjunction with another kind of investature. Once the second type has been tapped breifly (this creates the necessary "filter" to create a specific effect), the remainder of the energy needed can be provided partially or entirely by Ferrochemic Nicrosil.
- after burning a metal for ~1/2 second, the Twinborn can gain the desired effect almost entirely by ferrochemic power alone.
- can create Duralium-like results, as well.
-The exact abilities of a soulbearer, beyond this, are fairly unknown. The few hints given thus far indicate extreme versatility.
*A Twinborn of this form can be nicknamed a “soulburner”. Each of the individual types of soulburners would, of course, have their own names as well.
*The Second version is arguably not “Compounding” at all. I call it “Synergising”. Essentially, you burn one allomantic metal, and store the qualities it produces, via Ferrochemy. The result is an essentially endless supply of Ferrochemic power, which can be recharged Quickly. The following Twinborn combinations would be considered “Synergisers”:
Alomantic Ferrochemic Quality
Pewter Pewter stength
Pewter Steel speed
Pewter Brass wakefulness
Pewter Gold health
Atium Brass mental speed
Tin Tin senses
Gold Aluminum identity
Gold Electrum determination
There are likely other versions of this I have missed. The benefit is similar to compounding, though not quite as dramatic.
* I beleive Marsh used the Pewter-gold combination at the end of Hero of Ages. Without doing so, I do not see how he would have been able to survive his near-decapitation, as he cannot compound gold. I cannot confirm this, however, without asking Brandon directly.
3. Allomantically powering Hemalurgy -> Spike someone, burn spike, gain power!
- Major Boost in Hemalurgic quality stolen
- Major increase in Hemalurgic insanity, and vulnerability to emotional Allomancy
- Consumes Spike so you can’t have the ability forever, just until it runs out. Now you have to go spike someone else.
- Must be Misting of metal Spike is made of
- Spike must be placed in body to pierce the stomach. [must pierce the body in order to grant its hemalurgic effect. Must be contained in stomach to be burned.] This may or may not be a valid bind point. see post # 55
* These metals will alow access to second qualities, similar to the effect of 'compounding Allomancy to power Ferrochemy': Iron, Tin, Copper, Zinc. Nicrosil, Chromium, Cadmium and Bendalloy will do likewise, but the qualities they grant are unknown.
* These metals will alow allomantic bursts of power similar to that experienced through duralium: Steel, Brass, Aluminum, Electrum
*These metals will alow increased Ferrochemic ability: Pewter, Brass, Duralium, Gold
*I would nickname those who use this method "souleaters". The name comes from Harmony's explanation in Hero of Ages that "Koloss were not a combination of 5 bodies but 5 souls", thus hinting that it is part of the soul itself that is stolen during Hemelugy. (on a side note, this would indicate that 'Hemelurgic decay' is actually a very good thing, as it allows the soul to escape imprisonment)
4. Feruchemically powering Hemalurgy
*Unfortunately, Ferrochemically storeing a quality in a Hemelurgic spike does not grant any particular benefit, nor let you draw the Hemelurgic quality Ferrochemically. This is demonstrated in Hero of Ages when Marsh uses one of his eyespikes as a steelmind, but is not able to compound in any way by using this method.
*There is a theory regarding the use of a nicrosilmind, since that stores 'untyped' investiture. if the same metalmind were made into a hemelurgic spike, Ferrochemy should be able to power the effect of the spike. this is not necessarily possible with other metals, however, nor do we know the hemelurgic effect of nicrosil.
5. Hemalurgically powering Feruchemicemy
*The basic benefit here is the ability to share metalminds
*Process: Spike a Ferring --> Stab some with the charged Hemelurgic spike; this person stores a quality in the spike, or another metalmind -->Remove Spike, place in another person; this person draws stored quality from metalmind
*limitations:
- the initial Ferring dies, as per Hemalurgy
- removing hemelurgic spikes can be harmful, thus removing the benefit of sharing some powers
- must know Hemelurgic bind points
- must use a bind point that is not lethal to remove spikes from
- must use a Pewter, Brass, Duralium, or Gold spike
*larger Potential: true compounding of Hemelurgy and Ferrochemy (Theoretical. not confirmed)
- if two people are connected to one another by both being peirced by the same Hemelurgic spike, one could arguably draw Ferrochemic power directly from the other person (assuming the spike granted Ferrochemic power, and the apropriate metal was available to use as a bridge. You would essentially be forcing the other to store, while you drew power from them.)
6. Hemalurgically powering Allomancy -> This is done in the books. It's sadly mundane.
- This is the way Steel Inquisitors are made.
- You have to spike people, know bindpoints, lose power, etc.
- The person receiving the spike gains the permanent ability to burn a given allomantic metal
- If the person receiving the spike is the same type of Mistling as the power stored in the spike, the power stacks. This is how Vin gained the ability to pierce copperclouds.