These "ink pots" come in several heights and two shapes. There is this shape, with very rounded top and bottom shoulders and a rounded side too - the other shape has sharper corners and very straight sides.
They come with either polished-out round or oval pontil marks; or a completely flat polished base - often with a deep scar in it.
Sometimes, "Mdina" is etched in the polished rondel - in either Michael Harris' or Eric Dobson's writing.
It's a real shame these don't photograph as well as they look in reality.