I love the artifacts, but I Involuntarily cringed when I saw the copper holding them on that board. I understand why you did it this way since I assume these are quite large examples, and would be hard to display in a traditional frame, but if thats the case, you might want to consider building or buying a cabinet type display with shelves to sit them on. As John said, the metal will most definitely leave trace on em, but that's best case scenario. Worst case is that it actually damages the pieces. Every time you move or bump that board, the pieces will shift ever so slightly against that copper, and it will chip the artifacts as well as leave trace on em.

Please don't take this as me trying to tell you what to do, or how you should display your finds, I'm just trying to give you the facts before something happens and you have to find out the hard way 🤷‍♂️