I didn't have an answer for the other thread on cleaning pot metal but I do know a couple of good ways to clean gold and silver.
For unset sterling silver line a bowl with aluminium foil and sprinkle in a generous amount of bi-carbonate of soda (about 2 tablespoons or so) put in the silver pieces and pour over boiling water, watch the bubbles do there magic. use a soft toothbrush to get into grooves. rinse well in warm water.

for gold and gold set with hard stones, diamonds, rubies, sapphires etc.. clean in a mixture of one dash dish detergent, one dash ammonia and boiling water, use a soft toothbrush to get between the stones and filigree. rinse well.