The microscopic examination of a fragment of a fourth century A. D. glass diatretum from Corinth showed a complete lack of any refractive discontinuity in the region of the intersection of the vessel wall with one of the posts supporting the cage structure. It was concluded that the post and vessel wall were cut from one heavy-walled piece of glass and that the structure could not have been made by fusing together two separate pieces of glass. Chemical analyses are given for two colors of glass from the Corinthdiatretum, two from the Athens diatretum and a possible uncut diatretum blank in the Benaki Museum.