This post is one that won't give any new information, but will provide some clarifications on just how wizardry behaves in the setting. At first blush, there are a couple of counter-intuitive things that have been turning people off, and this post is going to serve as a reminder to myself to frame wizardry in a slightly different light.
First, an important distinction to make is that while I've been calling Aarnian magic "magic," I'm using the term in a very broad way. The word "magic" usually refers to something poorly understood, if it's understood at all. The process of understanding something, turning it into a science (as the Aarnian wizards have done with Aarnian magic) usually invalidates it from being called magic in the first place.
On the surface, Aarnian magic resembles classical fantasy magic, but when one takes a closer look, all the magic in Aarn could be redefined as psionics. It's powered by dreams, powered by the threads of an adjacent reality, and the fey could be considered inter-dimensional aliens. However, Aarn is a fantasy setting and not sci-fi, so I've used fantasy terms.
In effect, I'm calling it "magic" for flavor purposes, but very few other settings have approached magic from this same perspective. Magic is not something separate from what is real, or logical, or scientific on the planet Aarn. It's simply another fundamental law of physics, one that we happen to not have here in real life.
As for the magical energy itself - it flows through and saturates Aarn. There is ambient magical energy everywhere, flowing through everything, especially living things that have souls.
While the energy is everywhere, it is hard to control. A wizard's primary skill is harnessing and shaping that energy - that's the purpose of the spellweave, to keep the energy in check during the casting of the spell.
On the other hand, a wizard's material components - the physical objects required to cast the spell - do not power the spell. The components act as a key that tells the spell what to do. The amount of magical energy these components have in and of themselves is very small. Instead, the auras of the components simply resonate with one another in a specific way.
The resonating auras act as a catalyst, telling the rest of the ambiant magical energy what to do, and what spell effect to power. In a balooning chain reaction the spell is formed, and it's the wizards's job to guide the chain reaction and insure it actually does what he wants it to do once it manifests. The wizard must provided the appropriate spellweave to harness the chain reaction into the spell he wants to cast.
Because the components act as a guide - perhaps as a template or mold for the ambient magical energies, they are not destroyed by spellcasting, and can be used over and over again.
The few times that components are destroyed, such as in the creation of a potion, or the casting of a cheap scroll, they aren't destroyed because they are consumed by the magic for fuel, or as some kind of equivalent exchange - losing something to gain something.
Instead, they're simply destroyed because the chain reaction produced is too destructive for the components to survive with their auras intact.
In the case of scrolls that require a material component, the components are destroyed because runes self-destruct when they are used, and the auras of the components are connected to those same self-destructing runes, and are caught in the resulting chain-reaction of self-destruction. Very messy.
In the case of potions, the "material components" (which refer only to the objects that provide the resonance, and not to the water and its flavorings) have their auras and material composition changed beyond use by the boiling water and the chain reaction of magical energy.
Once the chain reaction has been started however, the components are no longer needed. As long as there is more water for the effect to "grow" into, more doses of potions can be made using the single helping of material components. Unfortunately, the more water, the slower the chain reaction spreads, and the harder it is to control it. Creating a single dose of potion can take only a few minutes. Creating a cauldron filled with 100 doses of potion can take hours, or even days.
Further, as the chain reaction spreads, it needs to be constantly monitored and guided by the alchemist. If his concentration waivers the batch of potion can self-destruct, or worse. This effectively limits the time that can be used to make a single batch of potion, preventing an alchemist from boiling an entire lake and using a single helping of material components to create a billion doses of potion. Alchemists have to sleep sometime, after all.
To keep these sorts of things in mind, I'm going to be more careful of my language in the future. A spell's "material components" will now be called "catalysts" in order to drive the point home of what they do - and what they don't do. This will also help distinguish the difference between the catalysts in a potion and, say, the water itself. The water is also technically a "material component" but because it doesn't resonante with any magical auras to produce the magical chain reaction, it's not appropriate to call it the same thing.
Also, as I've been doing in this post, catalysts that are destroyed in the process of making a potion or casting a scroll will be "destroyed" and not "consumed." "Consumed" gives the complete wrong kind of idea, and I blame it on a lot of the cognitive dissonance that exists in some of the previous wizardry posts, especially the potion one.