Gold bars can be made by smelting Gold ore in a furnace with level 40 Smithing. Gold bars are used to craft various forms of jewelry as well as golden bowls.
The Goblin Diplomacy quest rewards the player with a gold bar, and the Waterfall Quest rewards the player with two gold bars.
Smelting a gold ore gives you 22.5 Smithing
experience (33.5 Smithing experience with the Goldsmithing gauntlets equipped). A Mining level of 40 is needed to mine Gold ore.
Watchtower quest, an Ogre guard is bribed with a gold bar. In the same quest, a special gold bar is taken from Toban's chest, in the island west of Gu'Tanoth.
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Gold bars are also obtainable from
Strange Barrels, which are found within the Legends caverns
Pure gold bars made in Family Crest quest have a different item ID, meaning it's a different item but it can be used on everything that regular gold bar is used, with the exception of making Golden Bowls