Hi Anne,
If you can see copper/brass colour, then I think what Gingertom would suggest is that it is almost certainly silver plate, this is where the plate has worn away. If that's the case then it would not really be worth going to the expense of having it tested. Sorry.
If it doesn't look brass or copper in colour, just tarnished (black) then it could be silver, but for an item that size, and of that period, even if European it would be unusual for it not to have some sort of hallmark, even numbers such as 925 (92.5% silver)