There is a time and a place for meticulous prep work, undercoats and waxing and then there are also times when your mental health needs a bit of spray paint therapy.
Savvy Apron turned this old uninspiring looking kitchen-aid mixer into a super expensive-looking copper addition to any modern kitchen, with just spray paint!
You could probably do this with the radiators in situ (albeit with a lot of taping and dust sheets!), but this is probably best done before you actually install your radiators.