Plating the copper busbars in nickel will remove the possibility of copper oxidizing and tarnishing over time. Many commercial places plate the copper in either silver or in nickel for this reason. Some resources for nickel plating have been added below.
https://www.youtube.com/watch?v=2_jZCHQAPS4
https://www.instructables.com/High-Quality-and-safe-Nickel-Plating/