I was looking up something and was reminded of this 2017 incident. I sent a new collector a Constantine I coin. It looked like this-- when he got it, he decided it needed cleaning. It then looked like this-- he used nevr-dull...it is a great product when used correctly...I used a lot of it in the Navy for shining up brightwork (brass) and still have a can in my garage; which I use for chrome on my truck. So-- Nevr-dull...nevr use it on ancient coins...at least if you want the patina. Almost 7 years ago and I am still a little sad.
Another thing/ never handle MS/ Proof coins with your bare fingers. Saw one youtube video where someone from Numismaitique Genevensis held a 4.6M coin with his exposed fingers.
I tried to clean a Claudius II Gothicus Antonininus and I destroyed it. Before cleaning: After cleaning: Never again!
It seems a number of new ancient collectors like to start out buying coins to clean. In my opinion, this is most often a mistake. First of all, most 'uncleaned' coins are pretty near worthless anyway - either worn slugs or unidentifiable bits of corroded metal. And on top of that, 99% are common Constantinian AE's which you can buy in EF condition for $30-40. Finding anything of real value will happen about as often as you finding a 1909-S VDB penny in change. Second, cleaning coins properly is an art that takes a lot of skill, patience, and natural aptitude. Of course, practice makes perfect and you have to start somewhere - but it's not the sort of thing most people can just jump into and be good at it. It is very easy to ruin a coin! Just knowing when and where to stop and start during the process takes a lot of know-how and experience. Again, if gaining that skill and experience is important to you, then by all means practice! Nothing wrong with that. But if you are more interested in collecting coins themselves, I would strongly recommend buying cleaned coins from a dealer.
This guy on YouTube claims that he's "bringing some Roman coins back to life" by stripping them of their patina via electrolysis. Watching the massacre of these coins isn't for the faint of heart.....
That guy really has no idea what he is doing. Here is the last coin that I cleaned with electrolysis-- and after Maximinus II A.D. 310 Ӕ follis 26x27mm 5.9g MAXIMINVS NOB CAES; bust l., helmeted [with eagle crest] and cuirassed with gorgon on breast, spear over r. shoulder, shield decorated with two horsemen and four prisoners on l. arm. SOLI INVICTAE; Sol, rad. and in long robe, stg. facing, head l., r. raised, l. holding up globe, in facing quadriga; two horses turn l., and two right; in middle A. In ex. ANT cf. RIC VI Antioch 144
