Tiger, the dark internal patterned section is covered with fine bubbles, which is creating the shaded grey effect (you can see the real colour of the dark glass in the centre of the base pic), then there are uneven lines of larger bubbles running up the valleys. Uncontrolled bubbles rather than controlled bubbles I would say :lol:
So yes, it does have similarities to the swan. The eyes and the ears have been created using pincers and presses to the original clear casing, rather than being separately applied, likewise the beak is pulled from the original glass not applied.
Terry, thanks for the Ronneby suggestion, I'll have a look into that.