GE Mazda 240V 1000W Cobalt Blue Lamp

Here is a rather rare lamp I think, a recent eBay find. It is a US-made GE Mazda cobalt blue 240V 1000W incandescent lamp. Unfortunately the reinforcing ring is missing from the cap, so it is rather loose and has to be handled extremely carefully.

I was not sure whether to attempt to light it, but it got the better of me and I wound up the voltage very, very gradually on the Variac. I only went to a very low voltage though, didn't make a note but probably somewhere in the region of 75V or so for the photo here. I won't be lighting it again, this is very much a display lamp.

Can anyone assist with dating..? There is nothing visible anywhere, and if GE followed their common practice of putting the date code on the stem press, I'm out of luck unless someone knows more..?