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 or 33.5 Smithing experience with the Gauntlets of Goldsmithing 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.
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