stripping a patina Duster hood

I wouldn't even let it dry. It's much easier to clean up when it's still wet. Plus, if the metal's been DA'd and/or blasted, it shouldn't take that long for the phosphoric acid to clean up what little rust is left. Maybe it's just me, but letting it dry just results in more (and usually unnecessary) work. The "white powdery substance" isn't as easy to get off as they make it sound. From my experience, it's a pain in the *** to remove.

If it was me, I'd apply the acid, let it sit for 10 mins and wipe it off with a wet sponge and a bucket with lots of fresh water, then repeat as necessary.