Here is a cheat that works on all difficulty settings (Including the 5th difficulty)! You can get two or more of the same artifact!
Pick up any artifact that leaves behind a magic disappearance. Before the magic goes out completely, immediately go to the main menu and temporarily save the game. Now load that savegame and tada! The artifact is still there (Or the magical electricity is where the artifact is if close enough to grab it again). Repeat for a large supply (Helps to complete the 5th difficulty!)