Silfos works well with copper/brass. It is used in the refrigeration industry and is appied with a torch. Even a soft-medium flame from a small propane torch will do if the base isn't real heavy and absorbs to much heat. No flux is required, but the area has to be clean and the area has to be flooded with a flame to keep the weld from oxidizing as you apply the silfos. That's why the soft flame. Silfos melts at a lower temp than bronze rod but produces a very strong weld repair. It will have a more red look to it like copper, and will be hard like a bronze weld. A Dremel tool with a small drum sander attachment works well to shape and clean up the area welded.
