? about TY for a gift

We got an antique serving fork and what we thought was a knife in an old, velvet box. The person who gave it to us picked it up in an atique shop in England when he was there. We thought it was a carving set, but the 'knife' is way to blunt for that, so we're thinking it may be a cheese knife. I need advice on how to write a thank you to this person because we're not quite sure what the gift is. All we know that it is an antique thing and I'm not sure if it can be used or if it's something to show.

Thanks for your help!