I didn't weigh, but after I had pool of mild steel I added some copper - I guess about 15%. I wasn't really expected much, but it came out pretty amazing! Where I lightly buffed it it has a bronze look. I artificially weathered it and where I had buffed it did not rust at all! So seems to be oxidization resistant just like stainless and far more practical to make stainless from junk with copper than it is nickel and chromium. Seems like a really nice alloy so I plan to do more controlled ingredients next time. If you look closely, you will see some inclusions of a little quartz rock I crushed and sprinkled in the mold. It was a test to see if the molten steel was hot enough to fuse the quartz. Pattern was styrofoam carved by CNC machine, but I pulled it from the sand so not lost foam. I think I used greensand for this one. She hangs on my copper-sided house.
I think you'll find you have copper precipitated out of the steel on cooling. Ferrite has a very low copper solubility. You'll get more copper in solution in stainless. Interesting results.
Thanks. It does seem that way. It's interesting because where I buffed it does not oxidize, but if you want a rust patina you just don't buff it, but it is protected from oxidizing too much because the precipitated copper just under the surface. So its like you can have rusty stainless if that makes any sense!
...so on one piece you can have both copper oxide and iron oxide patinas - while only being superficial.
