Copper is the most versatile and durable of all metals and has been called "man’s eternal metal". It’s an amazing material for all kind of jewelry, and will last really long if it’s carefully stored. However, copper turns green after long exposure to air and moisture. Sometimes copper jewelry turns your skin green. It's known as the oxidation reaction. The copper reacts with oxygen in the air, your sweat and skin oils, creating a green layer of copper carbonate on your skin. It shouldn't be anything to be concerned about, it just looks terrible. Most likely you're not allergic to the copper, very few people are. Simply keep your copper clean and dry and remove any oil or sweat which may be on your jewelry.
When it comes to jewelry wire, copper is relatively soft and very easy to work with. It easily oxidizes with liver of sulfur or even hard broiled eggs and it looks really stylish and antique-like. Because copper is soft and when it is used in shawl pins is very important to harden the metal so your shawl pin will last.
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.
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. Depends on the shawl pin design, but many of those need to be locked and unlocked many times and be able to pierce some heavy or dense knitted garments and it’s very important for this piece of jewelry to preserve its shape so you will always enjoy wearing it. Don’t worry if your copper 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 copper shawl pins here.