I posted the same question over on tz-uk.. and have had some interesting replies:

"When I bought my TAG 1500 new in 1996 (correction 1996!) , i started noticing a ring of condensation under the dial within a few weeks and on closer inspection it was vaguely the same shape and position as the indecies.

It went back to TAG and they cleaned it all under warrenty and a letter came back from the service center saying it was a problem with the tritium used for the lume giving off something that misted the dial and was a known problem."

"I have a Zenith from the 70s and it has 2 radial, tobacco coloured marks on the dial, presumably from the lume in the hands. I know that it wasn't worn for a few years and the hands would have been stationery for a considerable period, so I imagine that's when it happened."

"My Heuer Silverstone did it. 'Smoked' the glass until it was almost fogged up completely. Very strange effect."

"I have a lot of vintage watches and never had the crystal clouding effect you mention although radiation burn is a very real phenomenon.

"I bought a vintage Rolex some years ago which had been a non runner for a number of years and you could see the marks where the hands had been stationary and burnt their impression on the dial."

Interesting that a Silverstone is mentioned, as I had it with a Silverstone too.. as did someone else who emailed me.. interesting!! Anyone else experienced it?

Stewart
- Heuerville