Trying experiments with High Fire silver foil.
1. (from left to right) - fired glass on High. The foil disappeared and left a slight sheen behind.
2. Fired two small pieces of clear glass on a Medium heat - the silver foil stayed. I was a bit worried about over fusing the glass again.
3. Fused the foil between 2 pieces of clear glass, and fused on Medium heat, for a little longer, until the glass melted/fused. The silver foil stayed - and still looked silver. This was the best method.