I got my replica CE28N rims with a rough powder coating, looked very nice at first and now after a few months they have this shitlike looking brake dust sticking around the spokes.

I tried scrubbing them with a sponge, it worked but only for the medium deposits. For the really black spots I can't do anything about them

I don't want to use anything more abrasive than metal brushes since my rims are the rough matte type.

Anyone came across this problem and came up with an idea...