Dear all, as the NOS topic has been quite hot in the last few weeks, here comes a question that has always puzzled me, so much more so since the Autavia bug bit me.
We know for a fact that a NOS watch is supposed by its very definition to never have been worn. Some items that are said to have spent years or decades in a drawer or in a case and so they must have been constantly shielded from light.

Still lume appearance changes a lot, from still bright white or even tritium-green to straw yellow to brown, most probably depending on the different materials, thickness of the lume itself and last but not least support whereon the lume was painted or applied. Sometimes we get to see the same model with different colours of the lume, and so I usually assume one has been exposed to sunlight and the other has not.
Anyway, and this has puzzled me, from time to time even NOS watches with completely crumbled lume are shown, as it the material had disgregated in aging.
This seems especially true of the filling in later Autavia, 11630's and 11063V's. I must admit that I am somewhat perplexed, as others from the same period like the 510.5xx that I love seem to have luming that ages very well.

Still my main curiosity is: what is the 'best practice' NOS lovers use in this case? As I assume the material does not evaporate, are the resulting crumbs and powder expected to be left floating on the dial or is the watch to be opened, cleaned and closed again? If so, how often? And as I know that re-luming is sheer heresy to NOS lovers, is leaving a blank spot the only option?
Cheers.
Fabrizio