Since you asked for mixed metals ,
Here's two rings I soldered together years ago.
Both bands are purchased sterling castings.
The skull is "carved" from copper , and the one on the right has a cabachon
I shaped out of Mike Sakmar Mokume Gane (nickel silver and copper).
Stay Brite is the solder I used , low melting point and flows really well. Its contains a small mount of silver too. Very strong stuff.
Craig