As I posted yesterday, I am experimenting with an ultrasonic cleaner to determine if using it actually damages coins. Note that we all know that cleaning a circulated coin reduces its attractiveness and value. Nothing worse than a shiny coin with VG sharpness - Ugh. But the purpose here is to determine if using an ultrasonic cleaner actually can damage the surface of the coin. As mentioned in this post's Part 1 yesterday, comments made last year when I asked the question implied that using an ultrasonic cleaner on coins would damage the surface by the action of the bubbles imploding on the surface or by some other unidentified action. Today, I selected three coins for experimentation. All three are shown below where the first photo of the obverse and reverse of the coin are the "pre-cleaning" photos and the second set is the "post-cleaning". To keep things as "scientific" as possible, I did not change photographic lighting or anything else and the photos have received no post-processing. All coins were immersed in the ultrasonic cleaner with a tap water and Dawn detergent mixture at about 130F. Then removed, rinsed in tap water and immersed in clean acetone for about 50 minutes, removed, air-dried and photographed. The only difference between the treatment of the coins is the amount of time the ultrasonics were applied. First up is an 1860 Indian Head cent in well-circulated and somewhat grungy condition. Six minutes exposure. The pre-cleaning photos and then post-cleaning: The coin is noticeably cleaner (not more attractive) and I cannot detect any damage to the surfaces of the coin. Next up is circulated 1854 Large Cent with about VF sharpness, dirty and some verdigris. This coin was exposed to 9 minutes of ultrasonics. As you can see, the ultrasonics removed some verdigris, but not all, and in the process exposed unreacted copper to the detriment of the appearance. Has the surface been damaged - maybe - look at Star 13, for example. A much shorter exposure might not have hurt the coin. Finally, a 1906-O Barber Quarter in about G-6 condition with some decent toning. By the time this coin went in the tank, the water/detergent mixture had noticeably darkened and some deposits were apparent in the bottom of the tank. More so after this coin came out. The quarter went in for 12 minutes but fell out of the holder at 11 minutes so test was terminated at that point. I'm only showing the obverse of this coin due to the 10 file limit but the reverse shows the same as the obverse. I think this coin's attractiveness was degraded by the cleaning, but again I don't see any surface degradation. So, what's the conclusion? I think if you want to use an ultrasonic cleaner to remove grunge and dirt, go ahead. I don't think you will actually damage the coin provided you set it up like I did to keep the coin away from being abraded by the dirt. My tests ran the ultrasonic cleaner for far longer than necessary - 6 to 11 minutes. Normally an exposure is about 15 seconds to 30 seconds. Always better to inch your way up and examine the results before giving it more. The results with the 1854 LC are illustrative of the dangers of excessive exposure. The cautions and caveats regarding cleaning circulated coins are clearly shown here. Two of the coins were not physically damaged but one was and they all came out looking worse, IMO. Comments are welcome.
Thank you for this post. I have oft wondered about ultrasonic cleaning. It appears your large cent exposed worse damage after the cleaning. I don't mean the cleaning damaged it, but it helped reveal the damage under the gunk. While I love what I call an honest coin; one that shows circulation but also good details, I also love blast white ones. I don't think your time and efforts warrant the cleaning. JMHO
thanks for posting the results of your tests. I'm not sure what the role of US cleaning would be. I find that a good long soak in acetone removes the organic gunk that bothers me. Maybe US is best for reserved for coins with adherent crust from being buried?
Thank you for this series, any more experiments on the way? If you can find a way to remove fingerprints from modern coins, without damaging the finish, I would buy that!
If I could figure that out along with the milk spots on Peace Dollars, I would probably earn millions. The acids in your skin etch into the metal of the coin so once a fingerprint is embedded, it's there forever.
My takeaway from these tests is that US should be used very sparingly and in most cases traditional methods are better. Acetone and Xylene are excellent at removing the organic crud that develops on coins and will not damage the coin. Water and detergents will also remove various organic and inorganic deposits. I think your point is well taken. There are coins that really cannot be damaged more by US than the damage that the world has meted out to them already. Those coins may benefit from the removal of encrustation in terms of preserving them from further degradation.
