I made two rings for a couple recently in 18k gold. They spotted a platinum two band ring on my website and wanted to have them made in gold. I began with two strips of wire, so I could use the left over gold to make the loop for the other ring. Hence each ring had a little of the others metal.
Here are the results.
Making process of the rings
Top Left: original platinum ring online
Bottom left: 18k rose gold ring with 18k white gold loop
Bottom right: 18k white gold ring with 18k rose gold loop