A gold necklace is made by using a gold bar on a furnace while having a necklace mould in your inventory or tool belt. It requires a crafting level of 6 and gives 20 experience when made.
Purchasing gold bars to make gold necklaces produces a profit of −181 coins. Crafting gold necklaces is one of the few profitable means of gaining experience that is available from a low level. Gold necklaces also sell fairly quickly on the Grand Exchange, as they are common Free-to-play items for players wishing to level up their Magic level by casting High Level Alchemy.
A plain gold necklace cannot be enchanted; only jewellery with gems can be enchanted, and the gem must be added during the crafting process, not afterwards.