Pitting is characterized by dark spots on the metal and is
irreparable. However, much of the rust left behind in the "pits" can be removed relatively easily by submersing the item in a bath of citric acid and water. Citric acid is a great tool because it's inexpensive and nontoxic and works quickly. To learn more about citric acid, click here.
Pitting is the result of rust eating through metal. Over time, small cavities, or divots, are created. Pitted tools can be cleaned, but it's not easy, and the damage caused by the pitting is irreparable. To enlarge the pic shown, click here.