A ring of forging is made by enchanting a ruby ring using the spell Enchant Level 3 Jewellery. When equipped, rings of forging increase the chance of successfully smeltingiron ore to 100%. Without the ring, the probability is anywhere from 50% to 80%, depending on your Smithing level. The bonus only applies when smelting iron ore in a furnace; it will not trigger when using Superheat Item, nor does it need to. After smelting 140 such ores, the ring will disintegrate.
The rings themselves do not carry charges; rather, the charges are kept with whoever equips the ring. Any player with multiple rings of forging can smelt 140 iron ore, regardless of which ring they wear, and whichever ring is worn on the 140th ore will disintegrate. This is useful in New Varrock, since rings of forging are hard to replace in the alternate dimension.
It currently costs about 12.2 coins for every iron ore smelted with rings of forging.
Operating the ring from the Worn Equipment menu will show the number of ores that can be smelted before a ring disintegrates. If wearing the Varrock armour and smelting in Edgeville, there is a chance that two ores will be smelted instead of one, the ring will only lose 1 charge in this instance.