Ring of forging

A ring of forging can be made by enchanting a ruby ring, using the spell Lvl-3 Enchant. If a player smelts iron ore while wearing the ring, it gives a 100% success rate of creating an iron bar.

A newly-enchanted ring has 140 charges. Each time the player smelts an iron ore while wearing the ring, one charge is consumed; after all charges are consumed, the ring crumbles. The number of charges is specific to the player, not the ring. This means switching, trading, or alching rings before 140 charges will not reset the number of smelts the player has left before a ring breaks. Players can right-click to "break" the ring, resetting the next ring the player uses to its maximum charges.

When using the Edgeville furnace while wearing Varrock armour, there is a chance to smelt 2 bars at once. If this activates while smelting iron with a ring of forging, the ring will only use 1 charge, meaning you smelt one bar for free.