Uncoated/Raw copper and brass are beautiful metals but they do tarnish (oxidize). Here's two methods showing how you can get it sparkling again. Once clean and dry a rub with a Sunshine Jewellery Polishing Cloth buffs it nicely.
1. Pour white vinegar and salt over the copper bracelet and rub in to remove all tarnish.
Rinse off and polish with a soft, dry cloth.
from https://www.sergiolub.com/blogs/news/five-ways-to-clean-your-copper-bracelet
2. My favoured method is a little tomato sauce, with a soft toothbrush, brush/rub and thoroughly rinse under cold running water. The brass earring in the photo show one tarnished and one cleaned with tomato sauce (any branch, but I use Rosella) and the copper bracelet below right shown partly cleaned.
Coated copper wire can get dirty from dust and wear. To clean wash it in warm water in a basin with mild dishwashing liquid. Use a soft toothbrush to get to those hard to reach places. Rinse and dry with a soft cloth.
DO NOT USE acid based cleaners of coated wire, or gold plating it will remove the coating/plating.