The fire focus gives your wand the abillity to shoot fire.
This focus uses 1 Ignis Vis per tick and shoots out fire particles. The fire particles deal damage and ignite any mob it touches. This wand does not cause fire on anything except mobs.
If not enchanted with Potency, this wand's fire damage on a single enemy (not counting the ignited enemy's burning damage over time) is lower than a wooden sword's damage. Note that it does affect every mob in a cone, so it becomes quite economical on packs of enemies.
If fired in short single tick bursts, it shoots one quick gout of fire that ignites all enemies in a cone. If used this way, the multiple-enemy damage over time exceeds all other wand foci for damage per vis (but not damage per second).
This wand core is completely useless against all nether mobs, but a wand that uses it often can be replenished by many nodes in the nether.
Thaumcraft 4.2 Tutorial [Fire Foci]
This video was created by Zautos.