Oh no problem with vagueness Leni, I feel just the same myself... I opened up Mark's book thinking I would find it straight away, and then to find nothing of that shape at all, I am now questioning my initial thoughts.
It is rather like the Aurene colours in an old IOW swirl I had, but that had a flame pontil (albeit rather smudged, it was nevertheless visible as a dent if nothing else). So I am doubtful it would be IOW, the base just doesn't look right.
Although to be honest, all the Mdina bases I have seen have been ground and polished, and this isn't.
So back to stage one.