I was given 2 Japanese kitchen knives that my sister in law never used. They were left in their original boxes for years and when I took them out, each has a small rust spot at the cutting edge. These are the sharpest knives I have ever used and appear to be handmade. Is there anyway to protect these blades? I will lightly sand the rust spot away, but is there an oil to use on the blade that will help protect it AND is safe to use on a knife that will be used to prepare food? Thanks.