Chinese Bone Pottey (Southern song) or 15th centurty?

by Oleg
(Upstate, NY 12442)

Dear Peter.

I think my previous post did not go through.

This item was described as bone pottery, Southern Song 12-13th century. I found on the Internet very similar item? also with a delicate carving inside. This carving looks like a watermark on a paper. This bone pottery technology was introduced in 1450's.
I have a pair. Do you know something about items like this? How about rarity?

I am placing a link to Flickr to see more details.

Thank you.

www.flickr.com/photos/63571741@N06/sets/72157626875679244/