I looked thru the latest thread on cleaning coins but did not see a specific answer to my question. I have had the below sestertius of Severus Alexander for 40 years. I would like to remove the black but don't want to harm the patina. I started soaking it in distilled water and brushing with a soft toothbrush a couple of weeks ago. The exposed patina has cleaned nicely, leaving a nice shiny green, but the black is going to be stubborn. Is soaking it in distilled water my only option? Is there a way to hurry it along. I would greatly appreciate some advice. I think this coin has some potential for being stunning!!
Looks to me like the corrosion will be tough to remove without harming the green patina. Maybe treatment with verdicare? I'm sure some other folks will be along to offer advice. In my experience cleaning coins you can only go so far with mechanical means (e.g., toothbrush, dental pick, etc.). It is also true though that your coin has better quality bronze (or orichcalcum) then late roman pieces which are easy to destroy in the cleaning process.
Second against cleaning it, problem is that black portion could be very well stuck to the patina. When using either bamboo picks or metal picks you run the risk of pulling off some of the patina with it, regardless of how delicate you may try to be, as it may have fused with it some regions. I'm not saying its impossible, but it is tricky.
So, don't pick at it!! But soaking it in distilled water would be ok, right?? That should not harm it, I would think!
You are likely going to risk losing the patina with any serious attempt. I don't think the water will do it. Hold tight, maybe a very experienced member on the forum has had some luck with this before. Good luck!
The thing with water soaking is that most contain mineral agents. From tap water to bottled, what could end up happening is it could reactivate the green meanie (bronze disease) if it is not properly dried and the water gets into little areas you can't reach. If applying water I would recommend a light swabbing with a Q tip of distilled water. Afterwards be sure to either bake the coin, catch some sun and try and dry it, or use a silica moisture absorbing pack (place it in baggie with it)
Here are some of the ones I have cleaned myself. I have used a various combination of tools from toothpicks, bamboo, dental picks, q - tips and gun cleaning cloths.
+1 I follow the general Antiques Road Show advice: don’t do it. Patina: “The surface of an object that has grown lovely though use and the passage of time”.
