Artistic Wire brand of jewelry wire is sold in many types, but almost all Artistic Wire has a copper wire core.
Natural Copper Artistic Wire is copper jewelry wire with an enamel coating to minimize tarnish on the wire. This wire will retain the bright copper color as long as the enamel coating is intact. By contrast, bare copper wire is copper jewelry wire without any coating and this bare copper wire will oxidize, turning first dark brown and over a long time ultimately turning greenish. Both Natural Copper and Bare Copper Artistic Wire will have a hardness of soft.