I would think for scrap value a wire brush would be the best way to get the big crud off. Beyond that I see no reason to clean scrap.

Now if it might be something that could be sold as a useful object then a bath of vinegar and salt works well. Might try a low wattage reverse electro plating to remove the outer layer. I have some experience with metal detecting and finding stuff you can't identify right away. So if you are not sure what something is then perhaps its better to hold onto it for now. Mike