@deaconbstl I was told it’s from an old method of making window glass called “crown glass”, it was manufactured by being blown into a large hollow globe shape and then flattened into a disk.The best window glass was taken from the outside where it was at its flattest and thinnest, what was left was the central part which contained the “pontil mark”. As this was cheaper but still had value at letting in light it was used in pubs and shops to save money while still letting in light