On Thursday, 21 July 2016 08:59:19 UTC+2, RichA wrote:

Given the speed, lack of ED glass then, I'd wager one element could be radioactive, with a nice 20-40% thorium oxide composition.

The once popular, Aero Ektar lenses were radioactive, I believe.
It was this which caused slow discoloration of the lens element.
I have the 7" F2.5 somewhere but have never used it.