I once bought a bottle of something called Novacan, which seems to work on Brownells Silvaloy which is a true silver solder. My one small bottle will last me and my family for generations, it doesn't take much. I presume you can still get it from jewelry suppliers. Properly used however, silver solder should be a very thin joint, almost invisible. The "thicker the glob the better the job" philosophy definitely doesn't work with silver solder. Lead/tin solders seem to darken pretty quickly on their own but the Novacan seems to work on that as well although I don't routinely use it for that.