Here's a shot of the commemorative McLaughlin mold shown at the San Jose National. It shows how the iron parts go together. Next picture looking down into the cavity is here: [id=180524938]

Remember this was heated up quite hot, but still the 2000 degree glass cooled when it hit the mold surfaces. Folds in the glass globs made the straw marks we all love to see. The glass glob was dropped into the mold and the threaded core half placed on top, plunging the core into the still molten glass. Trapped air made some of the bubbles during this operation.