Old Blast Deflectors Cleaning
 

I found that Steel Wool cleans old Blast Deflector Plates very nicely. Scrub under running water , perhaps some soap. Afterwards, add thin layer of 3 in 1 oil to prevent further oxidation. You’ll be amazed at the difference ! Pics say all, Before and after…
Both pics are the same one…..

A sandblastr works even better.
I have used that method or a Dremel with a wire brush wheel in the past.
Best way is to avoid it altogether via using a stainless blast deflector.

Actually, I don’t think I’ve ever cleaned one.

Do the best you can with what you have……