I have a pair of 18K? cuff links marked BOUCHERON PARIS. I need info please--?

These cuffs are marked with the eagle head & would be a great investment is solid. A quick search said that this hallmark is the most common one for French 18K. My question is this: Can they be plated or does this hallmark indicate 18k solid gold only? Also each cuff link is stamped with 2 of these eagle heads---any significance? Thank you for your time.