(I'm surprised and pleased that such an esoteric question is still interesting people!)
Patrick, no molds are used? How were the bosses shaped? What are "cast on bosses"? Were they applied? Cool bowl!
I think it's great that this forum is full of people who have personal affiliation with the glass industry.
"Gardner's discussion on the use of a skeleton mould has nothing to do with the lenses that you are so interested in." Sid, Gardner says, "The completed form had a pillared effect, surmounted by a row of convex shapes with a lenslike appearance." Sounds to me like it had something to do with it!
"The discussion may have lost focus on the lens forming" - not true at all!
OK, everybody, can you just keep an open mind for a wee while? Just try to understand this explanation? I'm not simply making up something that will fit my imaginary scenario, I'm drawing together the information that I've read about the glassmakers, these pieces, and the type of mold that at least two authors say is used to make this form of glass. As I understand it, they were uncommon, probably not used much in the last 100 years, and may not have been used much in Britain at all, so I'm not surprised that even glassmakers don't immediately think of them. I believe it's also important to look at all four pieces I've posted with these bosses to get an idea of the form of the glass, rather than going from a single image.
I must not be describing the technique very well, so I'm going to take another stab at it, providing visual aids. Please excuse my drawing! First visual aid (last image below, I bunged up the attachments) is something I mentioned in my last post: a glass object blown into a metal structure that become part of the finished piece. Where there are big holes in the metal, the glass inflates a lot, puffing way out, and where there are little ones it hardly sticks out the holes at all. The more restrictive the space, the less inflation there is. This is based on a piece I saw in A History of Glassforming, and the caption discussed this phenomenon. Makes sense intuitively, but it's important to understand for the rest of the explanation.
An imaginary visual aid: you're making a pizza, but before you stretch the dough out fully you put a cookie (biscuit) cutter on a glob of dough and leave it there. When you stretch the rest of the dough, the glob remains thick in the cookie cutter. Agreed?
Now for the real stuff (basically a repeat of what I said in my last post). The second sketch below is a (lame) drawing of part of a skeleton mold. I've termed the parts that make the ribs, "rib arms" and those that form the bosses, "ring arms." They are hinged at the bottom, and move inwards and outwards, and the basal ring plate locks them in position. The ring arms move independently of the rib arms.
A slightly inflated parison is put in the mold. The ring arms contract, "grabbing" a glob of the thick glass. The parison is inflated with the ring arms unlocked, so they move with the bubble as it expands, and there is little pressure on the glass in the rings to inflate. It is blown until the ribs are formed by the rib arms, then those are unlocked, the whole mold is opened up, and the item has its basic form. Then it's shaped and finished as necessary.
Can you all see now how this might work?
Just one more thing. I'm reposting a detail shot of the bosses on the pitcher, and also another Hawkes vase with bosses that I haven't posted. Notice how much more regular the optics of the bosses are in the second example, with hardly any distortion, and how the bosses don't stand out from the body of the vase. The glass is also quite thick. I believe these bosses were cut, not molded.