The other factor besides coppers higher melting point is the
source of your copper. Jewelry suppliers should be selling you
reasonably pure copper. Hardware store, discount store 'copper' or
electrical wire will be a lower percentage tarnish resistant alloy.
Hardware/electrical copper wire does not forge well either.
You say it does not forge well. I forge 4 gauge and 6 gauge round
wire into bracelets all the time. I use ground plain wire from Home
Depot or Lowe’s. I must say I haven’t any problems forging this
copper at all.
My searching on the matter reveals this copper must be 99.3% copper
or better with 99.95% being the norm according to industry standards.
Oxygen is introduced at a near 200 ppm to improve conductivity and
to remove/isolate impurities. This is modified by annealing and
forging. I suspect it’s resistance to tarnish is due to the solution
used in drawing or extruding the wire and is superficial only, for
this ability to resist tarnish does not survive annealing.
It’s true that electrical wire may be different than jewelry wire
normally because in jewelry wire there is no need to introduce
oxygen. I’m not sure we are talking about a great significance in
behavior for non electrical use.
Lapidary/Metalsmith (note, I used “Lapidary” this time.)
The Pacifik Image