This is one of my favorite recently-learned techniques. The technique is one of the featured techs in this month'sTechnique Junkies Newsletter. If you haven't tried it, you must as it is easy and loads of fun. I could spend all day working with my copper and each time the copper would look different. I have uploaded one example here usingArtistic Outpost stampsn on the faux etched copper background..
Here is a second card I made with the same technique. I like not putting anything on the background.