Teapot

[AciDBuRn]

[wev]

I know that they are silver for sure

And you know this how?

[AciDBuRn]

I checked with acid.

[wev]

Ah, the nickname should have been a clue. . .

Your test has told you absolutely nothing past the fact that the surface is silver -- as one would expect in sterling, coin, or silverplate. As in books and looks, it's what lies beneath that counts.

Both pieces are silverplate.

[antiquer]

Acid testing on silver is not very reliable and always damages the piece.
Just for a laugh, try silver testing acid on:
iron
pewter
lead
steel
Any of these can and have been silverplated. You already found the results of acid testing on silverplated Britannia metal.
Cheers, AinA