Anyone know anything about this piece?

I've got this gorgeous cobalt blue bowl and can't find any information on it at all. I know the pictures aren't the greatest - I do apologize.

The cobalt colour is actually a lot darker than it shows in the pictures. The design on the outside appears to be a very thin silver overlay. I did test it by polishing a small spot - the patina was removed but not as easily as I would expect with silver. I've tried everything to make out the hallmark on the bottom with no luck - I'm hoping someone here might recognize the piece or the hallmark.

The lady I got it from, who is 55 years old, said that it was her grandmother's. She remembers visiting her grandmother when she was a small child and seeing it. So I would guess it to be 55+ years old.

It's 8-1/4" diameter.

I also have a tall vase to match.

Any help at all would be appreciated!