The "proper" magnesiums need some special care when painting to avoid the magnesium oxidising when it's exposed to the air. The best I've heard of for refurbing mag wheels is Dymag. Not cheap though, about £200 the pair!! I don't think they discriminate against other manufacturers wheels............... You could try the likes of Dream Machine etc. but it's worth making sure they are going to treat them correctly and use the "special" primers etc. that are required
Do any of these places do a chrome look on the wheels?
I saw a black duke with shiny chrome wheels near the Kings road last week ... looked awesome, especially with the sun reflecting off the wheels. Must be biatch to keep em clean though.
The chrome look you're mentioning is probably polishing. I had my ally marchesini wheels wet sprayed gold in the centre and polished rims. Cost £135 per wheel + VAT + tyre fitting + balancing.
Yep. If the wheels are "proper" magnesium ones, then once they have been stripped they need some sort of aerospace primer applied to them before they touch the air.
The treatment for bare magnesium required before it gets painted or powdered is called a chromate conversion coating. There not many places that do this. If you don't you risk corrosion of the magnesium. The worst is that you don't see the corrosion as it occurs beneath the skin. I would strongly recommend to have it done properly. Many people get their magnesium wheels X-rayed periodically for corrosion and cracks. Failures of wheels are not considered to a fun experience.