Brass is an alloy of copper and zinc. On their own, copper will turn blue, green, or dark and tarnish rapidly. Zinc will also turn very dark. Together, they are much more resistant to tarnish, oxidation, and give very valuable properties.
When it comes to jewelry wire, brass is a bit stiffer than copper though its’ still easy to work with. It easily oxidizes, but liver of sulfur won’t work with brass. I personally like Jax patina solution which comes in different colors. If shawl pin is made with 20 or 18 gauge brass wire additional hammering or hardening is required to preserve its original shape and look.
If you make a shawl pin: Hardening can be done by twisting the wire beforehand, or hammering shawl pin or its parts. If you have a tumbler run 2-3 hour cycles with your shawl pin. Some designs require additional fine wrapping which provides some character as well as holding all components together. File all tool mars and sharp edges so the shawl wearer will not have any damage on her garment. Brass looks beautiful whether it’s oxidized or bare with a beautiful golden finish.
If you buy a shawl pin: Just by looking at the picture, you can see whether it was hammered or not. Don’t hesitate to ask the artist how durable that is. If you see shawl pin is made with 16 or even 14 gauge and not hammered, it will more likely stay the same with a long wear. Don’t worry if your brass shawl pin looks dull after some time, store it in air-tight plastic bag. Use a jewelry polish cloth to bring it back to shine, or simply clean it with lemon juice or ketchup, rinse it off with warm water.
You can see my brass shawl pins here.