I am grateful to Mikko, from Finland, who has done some research on the types of lume used by Citizen on their dials. Mikko was interested in vintage divers and chronographs, and managed to get this information from Citizen:

” Watch dials manufactured prior to 1999 may contain promethium. Near the bottom of the dial, if it does, it will state ‘P-Japan-P’. There are only trace amounts of promethium; however, with any radioactive material, it is recommended to avoid prolonged contact. If the dials do not have the marking, there will not be promethium in them. Not all dials pre-1999 would have the radioactive material.”

Promethium is a ‘low energy beta emitter with a half-life of 2.6 years’, so it would seem that there is little or no risk from our vintage watch dials these days.

Mikko was concerned as to whether radioactive lume was used on Citizen’s vintage divers – this was his main query, given he has got quite a number in his collection. It appears that it was not used on all but the 8200 models, i.e. the 51-2273, where the dial is marked          ‘P-JAPAN-P’. It also seems that Citizen never used the more active radium or tritium lume, only promethium.

I’ve added a note about this to the chronograph page – thanks Mikko 🙂

(Note: I first wrote that radioactive lume was not used on any of Citizen’s vintage divers, but I then noticed that it was used on the 51-2273 model with the 8200 movement. Please let me know if you see ‘P-JAPAN-P’ on any others)