Machining shouldn't effect hardness as you are only removing metal. You need pressure (ie forging etc ...) to increase hardness in Copper.
The unregistered one is spot on about the deep red oxidation. I am a Machinist/Metalsmith
and have experienced this first hand just last night while designing my own heatsink
from scratch. And I do mean from
scratch. Well, I didn't mine the Copper myself, but that's about it.
* smelting copper *
