I have made three earrings called jikan, which were made as burial goods in ancient tombs approximately 1,500 years ago, into necklaces.
They are made from copper or bronze, rolled into a pipe, and sealed on both sides. Sometimes they are plated with gold or silver, or wrapped in gold or silver plates, but these are rare and are specifically called gold or silver rings.
Due to the nature of the material, the surface is covered with rust (verdigris), so I polished two pieces and left one without polishing it, and attached the string as is. Of course, you can polish it if you like.