Instead of fusing, it created huge pits in the silver.
Oxidation on the surface of the sterling silver may be the problem.
Try depletion gilding the silver, i.e., raise a surface of fine silver
by bringing the sheet to annealing temperature and pickling a couple
of times, till the sheet has a powdery, white surface of fine silver.
Then brass-brush the surface with water and baking soda and keep your
fingers off of it.