To keep the walnut wood handle looking its best, wipe it dry right after contact with water. Water can damage the wood on the customized Swiss Army knife over time, so avoid soaking it. Every few months, rub a small amount of food-grade mineral oil into the wood; this helps prevent cracking. Use a clean cloth to apply the oil. For a deeper finish, apply beeswax and mineral oil once a year. Do not store the engraved Swiss Army knife in areas with high humidity or excessive heat. Clean the metal parts with a damp cloth, but keep the wood as dry as possible.