If you're heating and heating and heating, and the solder won't flow, it sounds like your torch isn't burning hot enough. I did have to use a bigger torch (bigger than my regular micro-torch) on these, as it's a lot of silver to heat. And, of course, the solder won't flow if the silver can't get hot enough. I learned that after wasting a lot of my time trying to make it work with my regular torch. It took forever, but did finally work. With the bigger torch, it only takes a few seconds to make the solder flow.