I have been painstakingly removing adhesive, paint, and rust from some very cool old tin I acquired from a renovated library. Current problem (after many, many, many): I used "Krud Kutter" rust remover and it left stains. I've tried washing with cleaner, buffing, putting more kutter on (which made the stains blacker), baking soda, sanding (which would work but would take WAY too long), wire wheel on drill (again, would take way too long and leaves marks). I've tried tons of things. Tons. Any ideas please?