This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
Both metal and copper oxidize when exposed to oxygen and this is a natural process. Copper that is exposed to the outside environment is more likely to turn green and that is why copper vases and decorative pieces in gardens are often green.
This is a chemical property of copper as it reacts with the air and moisture in the environment. If you take that same piece of copper and place it in a solution of ammonia, it will make that solution a dark blue, as it reacts with the ammonia.