Cleaning Coins

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!