You are correct in that Rose could be describing an incalmo piece. If it was, a join would be clear. The piece is more likely to be bands of colour applied on the gather. Just to clarify, Wirkkala didn't invent incalmo, he revived and fine-tuned the process that had been used in medieval Murano. I've never seen a Bianconi incalmo piece, not in Venini: Catalogue Raisonne nor the DeBono volumes. I think you are describing Pezzato, where the piece is made up of flat pieces of glass which are then fused together and blown.