I believe they are annodised as per majority of the RAY's split variety, BELGOM ALU is something I use on in particular for split rims, it's a good safe product with excellent sealent capabilities.
http://thepolishingshop.co.uk/acatalog/Belgom.html
Also do search on eBay there should be some sellers on there too selling the above product.
As already mentioned by (Muddy) Swisswax Wheel Brush an excellent brush, also their wheel clean another great product, it has no chemicals and in fact non of the Swisswax products do, very safe.
To endorse (H5's) comment, please, please do not use acidic wheel cleaner on any alloy wheel, regular cleaning with warm soapy water should be plenty, with the odd treatment of some sealent wax, especially this time of the year.
My standard RAYS have covered 19k now in 15 months and they still come up mint as they were day one, mostly thanks to their build quality/finish. My Bronze TE37's on the last car were a different ball game as again they're an annodised finish too and I made the mistake of running them through one winter, the salt managed to etch it's mark on the lips, took a long haul of oil treatment to reduce the damage, never again.