Copper in its natural state has a bright, metallic luster with a reddish-orange color. Over time, a "patina" develops that many people find desirable. At this point, the copper coating resembles the color of an old copper-plated penny.
In most climates, it is not feasible to "coat" the copper to prevent the patina from developing. The coating may become sticky or the patina may develop under the applied coating.
A simple mixture of household vinegar and a tablespoon of table salt, followed with polishing with a polishing cloth, will clean the copper. The patina will soon return so this will be an ongoing process. Something to think about if you love copper jewelry.