Soldering to something that is painted on is going to be a bit harder -- impossible -- because of the matrix. Good luck.
If it is really important, and you want to play chemist, you might consider one of the methods reported in 2012 to rebuild the contact with precipitated silver (i.e., a modified Tollens reacton). The methods use silver acetate or diethanol amine to give reasonably thick and solderable coatings. I suspect you are better off, though, in the immediate future with what has already been suggested.
John