Old knives can become rusty and dull, lose their edge, chip or become scratched. Restoring them to their original state takes time, patience and effort.
Clean the knife with penetrating oil and assess the damage. Use a brass wire brush to remove heavy rust and scrub the entire knife with a toothbrush. Dry the knife on paper towels.
Use wadding compound or a non-abrasive metal polish of your choice to clean away rust residue. Wipe the compound away after it dries.
Resharpen your blade using your preferred method. If the blade has pits or nicks on the edge, a wide, flat sharpening stone works best.
Shine the knife with jeweler's rouge and a soft cloth. Wipe away rouge with a second soft cloth.
Wipe entire knife with gun oil and dry with paper towels.
Vintage knife collector Fred Hunter believes that some knives benefit from cleaning. He states, "There are undeniably some knives whose condition cannot help but be improved by cleaning: those with rust so extensive and so unsightly as to be worth almost nothing in the 'as found' condition (Reference 1)."
But Hunter does not approve of restoring vintage knives, because "...so many serious collectors will simply have nothing to do with a cleaned knife...after a knife has been cleaned, you don't know what it looked like originally!"
Restoring old knives can affect their value if you have an antique. According to Gypsy Wilburn, "Rare blades have been ruined, even by museums, when attempting to restore them using the wrong techniques and products. The method described in this article is not for use on antique knives (Reference 2)."