Hi Jimmy,
You got me!
About 7 years ago, I was the first author of an article : Experiments With Radioluminescent Dials From IWC Watches.
For that article I did a lot of research, but I did not found that gamma-rays were capable to color glass. Glass is for a large percentage SiO2 and by adding elements such as Sodium, Borium, Calcium etc. the properties of glass and its melting point are changed. Enamel is for a large part glass but contains more minerals and elements than glass. Physically enamel will act very much as glass . I know this from my experience, when I worked as a young chemical assistant in a glass laboratory, at Philips, Eindhoven, The Netherlands , from 1963-1970.
Back to the "burning". The color of the stains , caused by Radium-226 paint is brown, varying from amber to dark brown. This is in concordance with the facts that you show on the old enamel dials.
The match ends : 1-0 for Jimmy.
Remarkable is the fact that I read about the reversibility of the coloring.
The "burning" effect can be reversed by putting the colored glass(enamel) in an oven at 300 degrees Fahrenheit for a couple of hours. In such way the "burning wound" developed during half a century, can be "burnt" away. I guess no watchmaker has ever tried to do that with an affected dial, but it would be worth to try this! Further , your quoted article makes clear that the affected material is obviously not radioactive and you thouht differently.
That is minor. (looking for a return match)
Kind regards,
Adrian,
(alwaysiwc).