In many versions of Terraria it maybe possible to clone items if the version you’re using has the ability to connect to other players worlds as well as the setting to disable autosaving (such as on the console versions like the xbox one and playstation 4).

In order to duplicate items follow these steps:

1. Have a player start a world and then turn their auto save off.
2. Join that players world as the second player, also turn your auto save off.
3. Drop the item on the floor that you want to clone, do not pick it up.
4. Exit the game and choose not to save.
5. Re-enter the game, you should have the item still in your inventory and the cloned item is still on the floor, pick it up and you have duplicated it. This will work with single items as well as stacks.
6. Save your game at this point, you must do this if you wish to again duplicate that item.

Once you are done, don’t forget to re-enable auto save if you wish to be on.