It is an absolutely stunning thing - what a desperate shame about the loss of the top.
However, there was an ordinary

tricorn bottle doing the rounds, minus its top part - cut off and polished just like this - it's image is even used as an illustration in many books. Sometimes it was described as an obelisk.
I would agree, it would have had to be towards the end of Mr. Harris' time at Mdina - in order for his skills to have developed and improved enough to produce this beauty.
"Seaweed" according to my (and I think Suzy's) "definition" is the teal blue strapping that is encased/surrounded by the yellow silver effect along with lovely golden bubbles - like bladderwrack, so yes, it is in the lollipops, but they have amethyst strapping inside too, so not pure what I would call "Seaweed".
