Am I missing something or are spirit binding materials good for binding any type of spirit? So if I buy 10 units of binding materials, I could bind (given the time and good dice) a force 5 beast spirit, a force 3 earth spirit, and a force 2 air spirit with those materials.

While Conjuring Materials don't have a type, they do have a Force. That is, as currently written you have Force 10 Conjuring Materials, that could be used to bind a Force 10 spirit of any type.

But it could not, for instance, be used to bind a Force 5 spirit. The availability of Conjuring Materials is Force dependent, you apparently can't combine 2 Force 3 Conjuring Materials and get a unit of Force 6 Conjuring Materials.

-Frank

That’s annoyingly inflexible, although it dose make a certain amount of sense from a balance standpoint, I guess you need quality not quaintly to bind high force spirits.

I would at least allow the binding of a spirit with lower force than the binding materials provided however.

Edward

I guess I imagined binding materials being as flexible as is dramatically appropriate. My group's mage doesn't stockpile binding materials, so it's not much of an issue, but we determined that the binding ritual for him differs greatly based on the spirit. So his materials would not be interchangeable for spirit type. But I would have no problem allowing him to combine materials bought separately up to the intended value, because we just figure that you pay more for higher Force materials because the ritual takes longer, and thus requires more stuff.

As far as I see, there's not much in the way of detailed rules in the book on this, and that's good. You go with what suits your campaign, your mage's tradition and whether you think keeping track of this crap is too much trouble. (I'd probably be stricter about it if our mage stockpiled supplies, but since he buys it on an as-needed basis, it's sort of a moot point.)