This is what my mom requested for her birthday this year. It's a circle of 16-gauge brass. I scaled down and printed this design, stuck it on with a gluestick, then incised the lines lightly through the paper into the metal with an art knife. After washing the paper and glue off, I used the incisions as guides for a permanent marker mask, sealed off the edges and back with wax, and dropped it into a ferric chloride bath for about 45 minutes.
On the back, the loop (a simple 1/16-inch rod) is secured with what I thought were very small beads of silver solder but which turned out to be more than enough once it was well melted.
I intended to give it a dark patina and brush back the raised knotwork, but none of my experiments with household chemicals worked. Liver of sulfur would've been ideal if I could get any. As it was, Mom said she preferred it with a bright burnished finish. Unfortunately, the texture of the spray lacquer reduced the glossiness; it would probably have been better-off with a painted lacquer instead.
The medallion is worn on a simple brass chain with a silver lobster claw closure.