G'day; I very much doubt if ammonium polysulphide is available in
shops; laboratory suppliers stock it. But calcium polysulphide is
sold in garden supply shops as a mild fungicide and lichen remover;
look for it in the fungicide shelves or ask for 'lime sulphur'. It
will blacken silver easily.
It is a yellow liquid smelling disgustingly of rotten eggs like it's
ammonium brother. Don't open it inside the house; keep it in a dark
bottle in the garden shed, or it will make the place stink like
blocked lavatories! Do keep it away from children. It is not
harmless, but there is no problem if it is used sensibly. Dilute it
with water as required.
Finally, sulphates such as ammonium sulphate are of no use in this
Have a lovely Christmas, hannukar or whatever.
Cheers for now,
John Burgess; @John_Burgess2 of Mapua, Nelson NZ