Some people like electrolysis. Since I assume this was found in fresh water, I'd go get some "iron out" at one of the big box hardware stores. It removes iron stain. "Zud" will also work. Put your item in a plastic container, away from people and animals, stuff is harmful, don't drink it! and then boil or just heat up some water. Put the water in the bucket with the chemical. I think I put the chemical in the empty bucket first and then add the water. Both give off fumes, so best to do it outside. Then you can either cover your bucket with something or lock it in a shed, which I prefer. Read the instructions. After a few days, take it out, let it sit a day or two in plain water to get rid of the chemical, then wire brush it. Some people then oil it.