I was reminded of this talking to @MiataMan00 -- Sonax Wheel Cleaner Plus will take DTC-60 / whatever brake pad dust in about 30 seconds.

I neglected to do a good before/after sequence, and now with COVID there's less opportunity to make brake dust

But lots of time to clean cars at home...

https://www.sonaxusa.com/best-wheel-cleaner.html

Race pad dust caked on for 5 months of sitting after track day (not a Miata):



This is after 1 minute of effort. It's totally safe for machined faces.

It's not fully cleaned, just trying to show the contrast between the parts of the wheel that have been cleaned and those that haven't.

Daytime clean shot:

 

Can confirm. This stuff is fricking MAGIC. I had years and years of brake dust, dirt, oil, grime absolutely caked on to a set of my track wheels. Im talking probably 3-4mm thick of just....****. The wheels were black. I was expecting it to soften up the top layer and have to repeat several times. Nope.

I sprayed the wheels down with some of this stuff, let it sit till it turned all purple. Scrubbed it with a rag for a few seconds, hosed em off and that was it. They look almost new. Absolutely fantastic product. I bought the Sonar Alcantara cleaner and its just as good. 12/10 products, will 100% buy again.

I wish I had before shots but again, I was skeptical so I didn't bother.

 

Adams wheel cleaner works as well, think anything that turns purple while it cleans is going to work.

 

I have a sonax similar product and just bought a K2 as well. Like Bronson said, whatever turns purple or deep red is an iron remover so the results should be good. There are similar products by many brands although I do feel happy with the sonax one as well. Not sure about the K2 yet.

People also use this process of iron decontamination on top of the panels as an easy alternative to the clay bar. It takes away only the iron sitting on the color though and not all the other grime.