Here's how to verdigris copper easy and using no toxins:
1. Rub a mix of salt and vinegar on the item.
2. Place in a closable box with a small container of fresh ammonia.
3. Leave for a while. It turns all cool.
4. Wash it off; as it dries it re-verdigris.
5. Seal it using a very thin layer of acrylic floor wax.