I have a (Brompton) frame which needs some touching up but most of the finsh is good. It’s an old gloss model and I think it would look wicked awesome in matt (Ivory/black).

Is it as simple as spraying with matt/satin lacquer?

What’s the best way to get a rust-proof and durable finish on any areas I am touching up? (STD Hellfrauds shake and rattgle, hammerite etc?)

Powdercoat?

Sorry just re read the diy bit.

Would fine wet’n’dry do it?

Wet and dry will matte it but also probably leave it very swirly, and it’ll be fairly tricky to get it consistent around the nooks. You might get a good result with a coarse polishing compound like G3… Basically follow the normal paint finishing process but stop early. Never actually done this but my orange is at this point in a mighty refurb just now and it does look alright.

Spraying new laquer over old paint can be a bit of a lottery tbh.