ok ... ok ... later is now ...
The weight fluoresced just like most "soda" glass items I have checked (in the clear dome, that is). That means under UV it is not possible to separate it from pre-Caithness Paul Ysart pieces, or most other 20s / 30s / 40s / 50s "soda" glass for that matter.
The colouring and working of the frit pieces were not, in my opinion, like Paul Ysart work that I have seen. The main point being that, apart from the various Badge weights attributed to Paul (some of which might even be Belgian!), all frit work of his that I have seen has been in neater, more rounded pieces and set on a thin white ground.
Also the finish to the base was reasonably consistent with other magnum sized weights I have seen which were most likely of German or Bohemian origin.
So I believe the weight is European, not by Paul Ysart.