BDG55, There has been a couple of discussions here regarding Sfumato v Polveri. My only take on this is that Polveri is dust and shows consistently across the work but it can have colour transitions in the work. Sfumato is more like smoke and the colour feathers into other colours in the work.
I have never seen this bowl of mine referred to as anything but Sfumato. See Leslie Pina - Archimede Seguso (a bit unreliable but just an example)
Still looking at the pieces regarded as Polveri I have, I find it hard to distinguish between them. This bowl does have a very different effect inside it to the bottom of it. The top breaks from a blue mottled, smoky effect feathering (sfumato) into a gold polveri. The base looks gold polveri all over. It is unusual and that is what attracted me to it.
Hey Ardy... There is much confusion about Sfumato as it relates to artwork and glass as the term has been used interchangeably with Polveri.
Leonardo Devinci developed, and was the most notable practitioner, of the painting technique, "Sfumato". He described it as, “without lines or borders, in the manner of smoke or beyond the picture plane.” He didn't actually use smoke but used the word as a description for the hazy, diffused, and smokey appearance that resulted from the use of the technique.
Polveri glass has a similar description but uses a different technique to the one Da Vinci used in his paintings: a gradual, defused appearance to the colors as they transition gradually into one another.
Sfumato glass is acheived by exposing the hot glass to carbon, ash and smoke which gives it its distinctive dark gray color. After the smoked portion is tooled into the desired shape, it's then cased in crystal glass.
As for the use of the term, "Sfumato" in Pina's, "Lace and Stone", she later, in her book, "Art Glass Century 20", corrected her use of the term, "Sfumato" and replaced it with "Polveri", which translates to "powder".
In her book, "Lace and Stone" page 69, Pina describes a particular pillow vase as Sfumato. However, in her later book, "Art Glass Century 20", page 71, she describes the exact same vase as Polveri, which better fits the technique of using powders to achieve the "Polveri" appearance.
Anyway, that's my 2 cents worth. :)