I thought I'd try an aluminum dioxidizer and etching acid to clean them and man what a difference, probably at least cut work load in half. Scrub wheel for 10 minutes with brightener and let soak for a few, viola. I used the acid undiluted and worked great, not nearly as harsh as caustic soda. The results were so good I had to try 2 wheels first just to make sure

The wheel face just needs a quick sand, polish and paint..... easy