Hello. I am hoping someone can help identify this Teapot's Mark. I believe it is Russian. The Teapot looks and is made very much like Sheffield Plate so I assume it is early Silver Plate, but that is my guess.
For more information about the double headed eagle in an oval see: viewtopic.php?f=24&t=18717 I believe the double headed eagle in oval could be an (unknown?) German or Austrian silver-plate mark.