We have trouble removing the carbon off the leads without etching and dulling the copper top. The customer wants the part bright as possible, but my bright EN bath can only do so much. I have also learned that other job shops have essentially refused to do this job, but I really could use this consistant business. Michael, if nobody comes up with a better answer, I have a thought. When you etch the parts, it only lifts the carbon residue.
Carbon is very noble.
If you can heat the part in air or oxygen for a few hours, or use a propane torch for a sample test. This will be a good start. There are carbon ashing equipment available that you can buy. That might be an expensive route unless you have substantial income from your customer. 1998 Mandar is quite correct - oxidation will remove the carbon but will oxidize the copper.