That's a beautiful, old coin with lots of detail. It's only my opinion, but I would use a long soak in mineral oil - not olive oil. Olive oil is dark; thus, it will darken your coin as well in the soaking process. I believe that olive oil also has a slight acidic base. Soak it in mineral oil and use the point of a tooth pick to concentrate on those areas were dirt is still bonding to the coin. Your patience will be rewarded. The longer the soak - the easier it is to remove dirt and other contaminants. That's a great coin!