This morning I was sawing out a star shape from a piece of recycled copper tubing. A the tube has been flattened I end up with two shaped pieces from one sawing session, which makes earrings a tad easier! The copper is tarnished and dull on the surface open to the air, however, as you saw you get lots of sparkly copper dust appearing.
Once the shape has been cut out there is usually a small hinge where the pipe is still joined which lets you prise apart the two shapes and have a look at what's inside. . .
This piece has a beautiful range of greens and once I've filed and sanded the edges I may well wax one star to maintain the patina and pickle the other to get a lovely clean copper.