If anyone can identify this it would be great, however I'm hoping more that somebody could please explain how it would have been made.
I've seen vases where the ribbon is trailed on the outside, but this isn't like that. The ribbon (for want of a better word) is internal, yet integral, to the vase.
If you run your hand down the inside you can feel it raised as it spirals down (tried to show it in second picture), but when you look on the outside the ribbon is flush as though its moulded.
There's a definite gap between the two colours of glass on the outside edge (third picture) and the bottom of the vase is not exactly

"neat"?! (fourth picture)
It measures 25cm tall, 8.5 across the top, and had a 6cm diameter base. It weighs in at 975g.
If somebody wouldn't mind taking the time to educate a glass-numpty I'd appreciate it.
Thank you.