A while back I bought some rusty files and somebody was talking about citric acid. They said they dumped in 2 or 3 small tubs in a bucket and left the files in for a week. I thought I would try it. My mom gave me a square plastic container that used to hold mush when she worked at the restaurant, holds about a gallon of water. I bought a small container of citric acid, I am not sure what size, maybe 4 ounces. I dumped it all into the water and stirred it then entered the files, covered it with aluminum foil.
After a week I took the foil off and found the files congealed together into one lump sum. I pried one off. It had a gooey black coating on that was impossible to clean. I decided to chalk that up to experience and covered them back up to eventually throw in the trash. Sunday I saw them again and pulled the cover off and one of the files popped loose right in my hand. It cleaned up nice and I was hopeful for the rest of them. Tonight I set up to clean them and found the first one too gunked up with a layer of white stuff to be cleaned. Way too much effort to clean. I rescued the screwdriver blank I had thrown in with the files and threw the rest in the trash.
I think maybe there was too much citric acid in the water.