Muriatic acid

Hyup, same uses as above.
With hard well-water, it makes short work of the scale. for 2 or 3 bucks a jug back in the day, it saved me from having to buy many a new toilet.
And Like said; it eats aluminum, so great for cleaning up piston-transfer in a cylinder. But man it's hard on the nose if yur not careful.And yes it will dissolve your fingerprints........