A diamond saw was used to cut out 3 circles from 3/4" thick glass for fusing together. The stack consisted of a solid top and bottom disk with a ring sandwiched in between them. Prior to fusing, the inside of the ring and inward surfaces of the disks were wheel engraved- partly in a style called "notching". Fusing temp was limited to around 1200F resulting in more of a 'tack' fuse (mechanical join) rather than full merging of the parts. A higher temp would have badly eroded the engraved shapes now trapped within.
Fine cuts were made to let internal pressure escape from the center space during firing. It worked- allowing the top surface to slump to a concave shape.
This is the last post on Traditional Glass Engraving series (and monkeys might fly out of...).