From my experiences and reading posts. I add an etch step before the DeOx-DeSmut when dealing with cast or unknown grades of aluminum. On the cast parts especially, the parts smut up in the etch step. Then the DeOx-DeSmut Takes it off before anodize. The only problem I've seen is if the parts are highly polished, it takes some of the shine out of them depending on time in the etch. I am using Sodium Hydroxide for my etch.
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