Cleaning an antique sword is tricky, as you want to remove rust to prevent corrosion but avoid overpolishing. A sword that is too shiny has significantly less value than one showing battlefield wear and tear. John R. Harvey, a writer for LionGate Arms & Armour, recommends removing rust with a light application of a metal scrub and then applying a layer of wax or oil to prevent future deterioration.
Soak the metal scrub in wax or oil, then lightly apply it to obvious areas of rust or corrosion. Rust is indicated by red, flaky build-up or a change in the texture of the surface of the sword. Take care not to mark the surface of the blade with the scrub after the corrosion is removed. Brush very lightly. Collectors who find themselves scrubbing vigorously to remove a spot of rust risk damaging the surface of their sword.
Soak the rag in wax or oil. Coat the sword blade and handle in a thin film of wax. Remove excess wax build-up with a dry rag. Wax and oil help bring out the sword's luster, and protect against future corrosion.
Store your sword in a dry place, such as a climate-controlled closet or above a mantel piece or wood stove. Do not store the sword in its scabbard--closed environments are prone to condensation and subsequent rust. Watch closely for the appearance of any new rust on the surface of the sword. Remove rust immediately with the metal scrub.
These cleaning instructions apply to carbon steel swords, the most commonly used material in antique European and American weapons. Japanese swords are made from delicate tamahagane steel, and can only be cleaned with plant oils. Modern stainless steel swords, which are designed primarily for display, may be cleaned with commercially made stainless steel polish.