I have some old roman coins that looked just like that. I took a plug-in type (small) battery charger, clipped the plug off of the end of the wires and replaced it with alligator clips. I put the coins (one at a time) in the negative side alligator clip, and an old penny in the positive clip, then hung them in a simi-weak solution of nitric acid. Now, the coins are clean and show all, or most of the details. The only negative part of this procedure is that the electrolosis also cleans the corrosion out of the pits, so some of the coins look pretty rough. I wouldn't recommend this for coins that have collectors value though.