Hello Dave - sorry you're being ignored ... everyone is otherwise occupied with our café debate

Welcome to the GMB by the way.
Having said that, regret I've not a clue as to the pedigree of your glass duck - doesn't ring any bells with me, but we have some members who collect hordes of these things and hopefully they might have an idea - fingers crossed. Rosie - are you there??

With my little knowledge of coloured glass would suggest that your reference to 'submerged' suggests you're thinking of the Italian equivalent which is 'sommerso' - a word used, usually, to indicate a colour beneath a clear casing - sometimes there is more than one internal colour - and this seems to have been, rather obviously as you can imagine, an Italian decorative invention. From what I can see of your duck, it appears not to be an example of sommerso - the colours appear solid.
I'm not aware that sommerso is related to submersive - but stand to be corrected. Sorry, but can't tell from just looking whether your duck was made with lead oxide or not, though something approaching 2.5 lbs. seems heavy for a duck, though from the dimensions you give the model sounds large.
Have also just noticed that this bird appear to be hollow - is this correct.