my friend cleans for me..He uses almost the same technique as this one... http://www.romanorum.com/docs/A Method for cleaning ancient coins. Romanorum.com.pdf
The process linked in #3 above is similar to the process I use. This Galerius, the original was so bad that I considered putting it in my junk jar. As you can see, with a lot of effort I was able to bring out most of the original detail.
Actual hands on physical cleaning was about 5 or 6 hours. There were sometimes a day or more soaking in distilled water.
