Rust buildup? Soak in overnight in vinegar and salt.
Ecotuinweetjes: Spade ontroesten en reinigen op ecologische wijze
want rust? here is a quick way to make some rust....
Using a vinegar bath to remove rust from tools (would work with bolts, screws, etc) - plus extra rust clean-up tips
remove rust from metal tools and found objects without scrubbing witha soak in this natural solution
Von Arx DK7 ontroesten dek - boucharderen - YouTube
FerroCon staal ontroesten primen
How to Restore Your Rusted Old Tools - PopularMechanics.com
Electrolytic File Sharpening Setup - Homemade electrolytic file sharpening setup comprised of a 12v battery charger, plastic container, and a stainless steel electrode. A mixture of water and citric acid is used as electrolyte.