Technically this doesn't mean that the ingredient used is destroyed, just that it cannot be used to cast spells with again. So using a horn as an ingredient when for a spell (like Stun) will not destroy the horn, but it will make it a horn that can't be used as an ingredient. For some ingredients you just remove it, like a Piece of Chalk, Iron Filings or a Piece of Cloth, because they don't matter much in the game other than as ingredients and are hardly worth anything, but a horn is worth something so here the players may have to make a note that it is magically burned out. Perhaps over time the horn can be used again as an ingredient.Once the spell is cast, the ingredient has been spent and cannot be used again to cast spells.
That is probably the easiest way of handling it.The way I interpreted the ingredients rule in the case of usable objects, like a musical instrument, is that it gets damaged during spell casting. It cannot be reused, unless repaired.
…just my opinion…
Could have sworn I read it (at least in the Swedish version) as explicitly stating destroyed, which would make sense as well. The force of the blowing of the horn made it vibrate till it burst or something like that. But I like the repairable version.That is probably the easiest way of handling it.The way I interpreted the ingredients rule in the case of usable objects, like a musical instrument, is that it gets damaged during spell casting. It cannot be reused, unless repaired.
…just my opinion…
One of the players actually become a spell-caster in our last session and we agreed that for small tiny items we use the resource rule. So for things like 'Piece of Chalk' or 'Iron Filings' the player have d6, d8, d10 or d12 steps of it and roll each time the use it. Other items, like amulets or crystal balls, are individual items (we went through each spell and decided what is what). Items that are used are destroyed. Worked fine.Likewise.We rule it as being destroyed (consumed by the magic).