I always thought gilding, particularly on vintage (or should I say vintique
) glass was highly prone to wear in a dishwasher. I would have thought it would take many, many washes to achieve this level of iridisation and then the gilt would have vanished.
So is there some air-borne chemical, perhaps a naturally occurring one, that could achieve this - I assume the presence of metallic salts that normally produces iridised glass. Perhaps it was left in a garden shed or something?
If not, then the only conclusion I can draw is that it was done deliberately as an effect.