Cleaning Coins

Summary of discussion on southasia-coins eGroup.
Included an older discussion from NUMISM-L

From: John Sanford 
Date: 1998 30 Jan 22:56:45 -0800

I have a few coins that I will be cleaning soon.
As an experiment I tried a couple different methods suggested to me.

1: Ultrasound. It did an excellent job at cleaning the
coin. The crud just fell off but I feel it took a little more off that
I would have liked. The coin came out with shiny spots. 
Maybe I kept it in too long I don't know.

2: I placed a coin in olive oil. It has soaked in it for over a month
and not much is coming off (or it is really slow). This stuff is so
hard it looks like it is encased in rock.

Is there a way to speed this process up or do I just have to wait?

From: Tom Kirby Date: 1998 30 Jan 1998 12:29:00 -0500 I think that ultrasound was discussed here recently, and it was not recommended, because of the brittleness the metal has acquired over the years. Olive oil is slow, but pretty safe. What you may be experiencing is a very thick patina
From: Sue Hazlett Date: 1998 30 Jan 13:57:30 PST My son got a bag of roman coins for his birthday that were all uncleaned. Many of them were really incrusted. He soaked them in olive oil for 3 months. The lightly encrusted ones cleaned up fairly well. We tried naval jelly and this cleaned up some other more incrusted coins. I finally tried a very soft bristled metal wire brush that I use on skis to polish off the hot wax. It worked great on the coins that we were ready to throw away as unsalvageable. I dip the coin in olive oil and then brush lightly, dip again and wipe on a paper towel. I have been surprised to come up with about half of the coins cleaning up to a point where they can be attributed. Some are even in F-VF. However, I have found that in some, but not all cases, the coins come out very bright. If a coin already has a patina, the brush will not rub it off. Some coins, especially the later ones, don't seem to have any patina, though. It is possible that if they were "new" when buried (sort of like a brand new penny) that they would simply become incrusted and not acquire a patina? Is there any way to tone down the brightness. My son actually doesn't care. He really likes the ones that come out looking like they had been minted a few days ago. Personally, I enjoy cleaning these coins. It's kind of a neat treasure hunt. I sometimes wonder though, what the original owner would think if he knew the next person to see his coins as he did was 1600 years and half a world away!
From: Dr Gyula Petranyi Date: 1998 Jan 31 12:26:49 +0200 Olive oil: To speed up the cleaning process the temperature can be raised but you need some thermostat to keep the temperature around 56 degree Celsius which is still bearable by hand. Easier to find thermostat cabinets that maintain 37 degree Celsius, the temperature used for bacterial cultures. Don't use gas burners or ordinary electric hotplates or herds to heat the oil!
From: Jxrgen Sxmod Date: 1998 Jan 31 You cannot discuss ultrasound, unless also to discuss which solution you are using. I have not tried it yet, but maybe someone would try to clean a bronze coin with with a bath of olive oil in ultrasound. After then - if necessary - bruch the coin with bee's wax. Let's hear the result. I have cleaned encrusted basesilver by placing the coin in a galvanic bath as cathode, a piece of stainless steel (an old spoon) as anode, a solution of 1% H2SO4 and 9 volt. The coin was cleaned within half a minute. If you want a real silver colour, then boil the coin in a solution of 1 liter water, 30 gram tartar and 30 gram NaCl.
From: Ken Dorney Date: 1998 30 Jan 11:24:36 EST Olive oil is an old cleaning agent that some swear by, but it can indeen take many months to do the trick. You have to decide whether the coin is worth the wait. Also, those hard encrustations often will not come off, unless you resort to mechanical cleaning.
From: Shailendra Bhandare Date: 2000 Jun 30, 11:41am > Rajat Bedi wrote > Please advice how to clean the copper coins. Cleaning methods depend a lot on what is the composition of the patina that a copper coin bears. For 'bronze disease' or 'verdegris'(the green powdery substance that often ruins a coin)I recommend the method, perfected at the Birla Archeological and Cultural Research Institute, Hyderabad, and reported in 'Coins and Archaeology', papers given at the 2nd International Colloquium, IIRNS, Nasik. This method requires a good amount of distilled water and is fairly slow. But it removes the verdegris permanently and affords protection to the copper surface so it does not recurr. The method is as follows - A reagent called 2,4-AMT (full chemical name 2-amino-4-mercaptothiadiazole)is required. This is available through E.Merck, the supplier of analytical chemicals. In India, about 2 years back, it costed 4500 Rupees for 50 gms. Take 3.3 gms of this white crystalline powder and dissolve in 1 litre of distilled water.It is sparingly soluble to stir well to dissolve. This will give a 0.1M solution. Take some of it in a beaker and immerse the coin to be cleaned in it. Adjust the pH to 4.6 by adding a few drops of glacial acetic acid.Check using a pH meter, or pH paper.At that pH, the reagent reacts with verdegris and forms a curdy greenish yellow precipitate.This is formed when the reagent forms a chemical complex with verdegris. Allow time to complete reaction. Wash coin with copious amounts of distilled water. Repeat till no more precipitate is formed. The reaction is slow but may be hastened by keeping the container in a boiling waterbath. Heating directly is not recommended because that decomposes the complex formed between the verdegris and reagent. As the process is specialised and somewhat expensive, it is recommended only for coins which deserve it!