Ancient Specialists: What Cleaning Do You Consider Harsh?

Depends on the metal. Bronze is usually cleaned with distilled water or olive oil, and brushed with a toothbrush or picked with a non-scratching object, as DavidUK mentioned. Some use electrolysis as a last-ditch effort, but it ruins the visual appeal of the coin.

Silver is hardier and can safely be cleaned with chemicals. I have never done it, but some apparently soak silver coins in windex to dissolve the dirt off.

Gold of course is nonvolatile and can be tossed in a vat of acid to remove encrustations.

Silver-plated (silvered) coins are more delicate and shouldn't be cleaned by a novice.

All that said, the "1 uncleaned genuine Roman coin" listings on ebay are criminally overpriced for what you will get. Go for small lots or individual coins.

Impatient people should have nothing to do with ancients, for they will destroy more than they know. Many times a neophyte, who struggles with recognition of language and imagery, thinks that the encrustation is the reason s/he cannot "read" the coin, when in fact that person might be mystified by a clear example. But when that failure happens they cannot clean the coin fast enough, and it gets abusive treatment.

Ancients may be cleaned and cleaned very well, but only if you are patient and familiar with the effects of various chemicals and methods. Let me illustrate. Here is a silver coin that was offered recently, for which I paid a couple of hundred dollars in this condition.


The coin is basically well preserved, but disrupted by patches of encrustation. How does one go about removing something like that on a coin that is not a "throwaway? At this price point, many collectors would be unwilling to tackle further cleaning. I'm not that bright, so I went ahead and applied my tried-and-true method. It is still a work in progress, but here is the reverse, before (on left) and at present (on right):


The work still has a ways to go. The image on the right is lit somewhat differently, but the patches of encrustation are significantly reduced without significant disruption of the coin surface and no staining. Where I have worked on the encrustation I have been able to take it all the way down to the silver surface, but not below. The method used for this is direct application of a sharp steel needle to the encrustation while viewed under a microscope (10x to 30x). If I could match the lighting angles exactly you would see that there are no new scratch lines visible on the surface of the coin.

In order for that to be true, the pressure on the needle point must be so light as to have little effect in each movement. One does not remove masses of material that way, and it takes a while. Yet when it is completed, I believe this coin will be significantly improved without altering its original surface in any way.

That I think should be the goal of cleaning, and the guide to the approach one uses.

I've had good luck with electrolysis. It gets a lot of the chunks off before olive oil forever.

I agree that this doesn't make sense. Thermite burns at something like 4000°F. Seemingly there are plenty of other better ways.