I am a bit baffled as to what occurred to the bike here. It is actually hard to make things rust significantly and it is relatively easy to protect them. I.e., to get this kind of rusting, you would normally need to keep a bike parked outside under elements for months, maybe a year+, and not give it any sort of protection. Water readily creeping under the lacquer and staying there indoors??
Hi thanks for your reply, the bike has always been parked indoors: both when at work and when at home. We both don't manually dry our Brompton after a rainy ride (with clothes), but let them just dry indoors like all our bikes. (we both own four bikes per person) In winter time roads are treated with salt here in The Netherlands, but my own 28 year old Brompton has no single spot of rust while traveling in winter time. (this bike has a red / black lacquer)
The interesting observation is that other parts than the bike frame of my girlfriends bike frame are mostly free of rust like spokes, brakes, rims, whereas my own 28 year old Brompton which I bought secondhand 3 years ago has no single spot of rust on its frame but has several parts like some bolts which show rust.