my excuse - should I get it completely wrong - is that I can't see the picture very clearly

...........but, opaque/etched/vaseline it is almost certainly not. Would imagine that the textured surface of the mould was such that it has produced a frosted finish on the underside of the glass (the top side appears shiny to me) - thus creating a translucent effect (i.e. allowing the transmission of some light, but in a diffused way). This shade of green looks wrong if there had been some uranium present - and as you probably know, the only certain way to prove this is to use the u.v. torch. Do have one?