Explosions are actually caused when an item boils, not when it ignites. I've done some extensive work in trying to make explosive critters, and if you just make them drop something that ignites you'll end up with !!material!! just sitting there and smoking up the place. And it'll sit there for a very long time.
Booze explosions (I've had the good fortune to encounter one of my own) are composed of "boiling dwarven wine", rather than "!!dwarven wine!!".
As for the dwarven pitchpots (magma-warmed bolts), that's an interesting idea. Even more interesting is that it could actually work, since a burning projectile will light other items on fire when it gets embedded in a creature's inventory. Unless they're quick about pulling them out, they'll have a large helping of !!death!! on their hands.
But it may annoy any woodworkers who made masterful bolts, and it will also litter your battlefields with smoking rubble that may take years to burn out. Unless you've got a master flood switch, that is.
But I don't know what effect magma has on the temperature of adjacent tiles.
EDIT: Okay, I'm currently working my way around some arachnid-type critters, and I was wondering about a couple things... Should I add [SEVERONBREAKS]? It makes sense for a creature with an exoskeleton, but it might turn up with some peculiar messages from time to time. Also, should a spider's bite be GORE or PIERCE?
The reason I ask about PIERCE is because it will cause peculiar messages if the spider happens to be shaking something around. If I put it in as PIERCE, then I think I'll just remove the CANLATCH flag so that those messages don't show up.