The protective green patina which forms on copper when it is exposed to the atmosphere is complex and has been poorly characterized. Using modern analytical techniques, more than 15 samples of patina of varying ages and exposures have been examined in detail. A number of new components of copper patinas have been revealed, and the results, combined with atmospheric chemical information, have been used to deduce detailed mechanisms of patination. The previously established physical and chemical characteristics of copper patina are reviewed. The design of the investigations reported upon in subsequent papers is described. -- AATA