A couple pictures to assist with the recent discussion. Based on looking at this insulator it is apparent that it was made in one piece (no sign of a seam where a base was applied). The mold line also tapers off where the base would have been curled in, which would be consistent with heating and handling required to curl the glass under. It was an excellent job, but you can see some indication that it was hand rolled and not molded. Use "view original" to get a closer look.