Hi, newbie here, hoping to get some assistance. I found this heavily tarnished metal handled
It looks as if it probably is, or rather was, electroplated nickel silver (EPNS). The black tarnish would have been from the silver coating. The metal polish which you have used appears to have completely ruined the silver silver and exposed the base white metal. The silver plating may of course have already been breaking down when you bought it.
I presume that this footed dish would have been for a fruit display. The central depression may have been intended for a larger fruit such as a pineapple.
If you don’t mind removing the plating then I suggest you carry on as you have been doing; there are no easy short cuts.