Trouble with Ultrasound

[styxman]

OK, I am lazy. While I can clean a coin remarkably well, it takes a good long time. So, I went in search of a quicker – easier system. I have seen ultrasonic cleaners supplied by various numismatist related shops and figured this might be a way to go. So, I obtained a 3.5 gallon, 450 watt ultrasonic cleaner that also has a 450 watt tank heater – I thought I could find the correct combination of pre-soak followed by a period of ultrasonic cleaning. What I found was disturbing and want to get your thoughts.

My approach to this topic was to photograph sets of coins (usually Wheat Cents), subject the sets to a variety of cleaning parameters and take another set of photographs. Parameters includes which cleaning solution to use, (only used distilled water), duration of pre-soak at what temperature and then exposure to ultrasound for a period of time. No more that five coins were cleaned at one time to assure that they did not collide against each other in the cleaner.

I found that exposure to ultrasound for as little as 1 minute results in a deformation of the coin. Roughly %90 of all coins showed new defects, some showing large areas while others showing only very small area. The defects had the appearance of being sandblasted with a very fine sand. While I have no idea of what this is called, I made up the name Cavitation Defects. Has anyone else seen this? Is 450 watts too much power?

I have looked for other descriptions of problems with coin cleaning using ultrasonic waves but have found nothing other than damage with coins bouncing into each other. There are many references on the LCF of members using ultrasound – I must be doing something wrong.

Images uploaded show the Cavitation Defects from three coins – some with labels as well as Pre and Post Ultrasound.

Thank you for your time and thoughts!

[Roller]

I have used a cheap jewelry cleaner (ultrasound) for years now with no such effect on coins. The power of yours may have something to do with it but you have to understand that an ultrasound cleaning would not guarantee a uniform surface. The ultrasound will remove debris but it will not renew your coin. The areas that show the light spots may have had debris on them that responded to the cleaning. The spotty surfaces you see are what were under the debris. Just my 2 cents.

[kloccwork419]

What are you cleaning them in? What solution?

[styxman]

kloccwork419, thank you for your interest. Here is a list of the cleaning solutions I have tried:
1. Water (distilled)
2. Dawn Professional Liquid Concentrate
3. Formula 409
4. BrandMax Tri-Clean
5. Blitz Gem & Jewelry Cleaner
6. Isonic Jewelry and Eyewear Ultrasonic Cleaning Concentrate
7. Elma Tec Clean
8. Alconox Cleaning Powder
9. Cucins Concentrate Dish Detergent
10. Master Fluid Solutions Stages TM Clean 2020

Distilled water used as a diluent in all the above.

I am running some more coins through cleaning and another set though the Ultrasonic cleaner to see if I can find what Roller has suggested. Maybe the bright copper areas are just underlying the dirt/debris on the coins. So far, I have not found any "sandblasted" areas without ultrasound. I will be able to upload the results soon.

Please let me know it there is anything else you want to know about this whole ultrasound thing.

Over and out, styxman

[Roller]

Use absolutely nothing but water. I am not familiar with the alcohol cleaning powder but I'm sure it also has chemicals/binders other than just alcohol. Jewelry cleaner will absolutely destroy the patina of a copper coin and much worse. To give you a heads up, with coins that have caked on dirt, I first soften the debris with some Verdi-care (just a drop on each side of the coin will do as long as it is all covered). Depending on extent of dirt, I may keep it in that solution for as much as an hour (there have been times when I forgot to remove it for over a day and nothing adverse has happened). I hold the coin in a ss bar shot measure, glass will do just fine also. There are times I use hot water. Put in cleaner for about 5 minutes at a time. I sometimes repeat this process (if the coin is worth the effort) until I'm satisfied. Sometimes the crud needs some agitation from and instrument to dislodge it but this is a very delicate process and I would not suggest you try it on a valuable coin. If you do want to try it, do it right after you take the coin out of the Verdi bath while it is still wet. Smash the end of a toothpick until it looks like the business end of a broom and dip it in the Verdi before using. Do not touch the surface of the coin with the pick just agitate the pool of Verdi that will form over the affected areas. I do this under my microscope to get at the creases in letters and numbers. Keep in mind that the ultra sound is just for removing debris stuck to the coin not to re-finish the entire surface, something you don't want to do and something that will happen when you use any of the "cleaners" your list.

[styxman]

Thank you, Roller, – I have been using only distilled water in the ultrasonic cleaner for some time now. The vast majority of the cleaners are from my lab where we use an ultrasound cleaner to wash our glassware, surgical instruments, and other equipment. The Alconox Critical Cleaning Experts is a powder that you mix to a %1 solution to use in an ultrasonic cleaner which works wonders on glass. It produces a mild alkaline solution which seems to be fairly hard on cents. It was quickly eliminated as a possible cleaning agent. What worked the best was the BrandMax Tri-Clean Triple Enzyme Cleaner as a bath prior to cleaning but did not save a significant amount of time off the cleaning process.

Cleaning coins is a hot topic but has been an area of interest for many years. I abandoned the use of wood as a probe to dislodge dirt/debris from a coin a long time ago as the potential to mar the coin is too great. I found in my hands that toothpicks are one of the worst (Bamboo Chop Sticks are better) as they often contain metallic fragments from their manufacturing. If a toothpick must be used, then you have described a method where the potential damage is kept to a minimum. Many many other materials have been tested and a few found to be safe and effective in the cleaning of coins – more on this topic much later. I also use the microscope when cleaning all my coins.

Your comment on the bright spots being exposed after removing the overlying dirt/debris was worth a second look. I can not recall having a bright area appear during my old, slow and tedious method of cleaning, but maybe I wasn’t looking hard enough. I selected two shotgun rolls of wheat cents to be cleaned with a watchful eye towards any bright / shinny areas; one roll cleaned with use of ultrasound, the other with the old way. I found the spotty surface as you described – something we have noted for years with the coins cleaned the old way. No bright sandblasted areas were found. I returned to the ultrasonic cleaner and immediately found the bright areas. As there have been no collaboration of this hypothesis I can only assume that I am doing something wrong or the power of the ultrasonic cleaner to too great. I might try a weaker powered ultrasonic cleaner at a later date, but I am going to abandon the use of ultrasound for now.

Thank you again Roller for your insights – worth much much more that 2 cents.