Hi David thanks again, there is not a lot of sfumato, mainly around the neck. I always think it is more like dust than aventurine and it always looks as if it has washed in there with some areas heavier than others and trails where it hasn't been covered properly. Luckily one of the first great A.Seguso pieces I bought was full of it (Pulveri Oro) and I had to find out about it. This is the quote I originally looked up:
""Sfumato" is a technique producing this smoky effect by enclosing fine inner veils of colour in the glass."
It is usually over the top of the main colour or gold foil.
I bought this piece for using and not really for the colllection so it doesn't really count but it still a lovely lamp and a great piece of glass.