Oil is used to prevent the rust of the Japanese sword. Oil makes a film of the oil between the sword body and the air, and it prevents the oxidization of the sword body. Oil dries inabout five months. Therefore, reprint it in the new oil once in three months. Oil a sword body by using the thing which cut a Nuguigami and flannel into the suitable size. (The absorbent cotton and the leather of the deer as well are being used.)