Vinegar that is a new twist for file re sharpening. The traditional method of dip sharpening over here has always been Lead Acid Battery Acid, to move things along a little quicker a slightly stronger mix of Sulphuric Acid 35% Acid 65% de mineralised water. Another apprentice job for me in past times it did take me some time to work out how I got the holes in my work clothes after they where washed. The files where left overnight in the Acid then rinsed in water then left for a couple of hours in washing soda to neutralise any Acid residue. Sharpening files is a sort of long gone practice because the cost of new files today is a fraction in real terms than in the past, Now it is just use cutting tools until the edge has gone them throw them away this culture has come in rather than re sharpen in modern engineering.
