I must admit, I take the easy route, but it works. I do a bit of conservation and mounting work. Here is an actual example and the method used.
This applies to in ground iron, not salt water finds.
I wash the item in hot soapy water, then I soak it for app. one week in a plastic bucket, during this time, I take it out every day and wire brush it. The next step is to wipe it and then blow dry it then bake it in the oven at 200 degrees for about 4 hours. Now for the finishing. Give it 2 or 3 coats of Rustoleom Rust killing primer. Next spray it with Rustoleum flat black. After careful inspection you can now mount it. The finished product of this example is below. Frank...