Charge Fire Orb

Charge Fire Orb is a spell in the standard spellbook, requiring 63 Magic to cast. It may only be cast on the Obelisk of Fire, located deep within Taverley Dungeon, and is used to turn unpowered orbs into fire orbs. A charge-all option is available, and each orb charged will consume one set of runes. Because the spell requires 30 fire runes per cast, it is strongly recommended to use a staff of fire or equivalent when casting it.

The Obelisk of Fire may be most easily reached by players with 80 Agility (boostable), who can take the second of Taverley Dungeon's two Agility shortcuts. Otherwise, players will need 70 Agility (boostable) for the first shortcut, or a dusty key, to access the Obelisk. Players without the Agility requirements will have to run through the entire dungeon to reach the Obelisk, which takes a long time. The Obelisk is located west of the dungeon's black dragons, which are not aggressive.

Assuming all materials are bought on the Grand Exchange and a staff of fire is used, casting Charge Fire Orb currently yields a profit of coins, or  coins per Magic experience gained.

Cost
Charge Fire Orb Charge Fire Orb Charge Fire Orb