Answer
It is permissible for women to wear any amount of silver in Salaat, be it pure or imitation.
It is not permissible for males to use rings of any metal, gold, platinum, etc. However, a silver ring equivalent to 4.5 Mashas (67.5 grains troy) is permissible.
and Allah Ta’ala Knows Best
Mufti Ebrahim Desai