Question about Olive Oil mon Coins

Somewhere I read a while ago where a person had recommended olive oil as a way of cleaning and preserving very old coins, copper, bronze or zinc, anyway, on the grounds that these coins were constantly exposed to olive oil from the fingers and hands of ancient people and it would not harm them and may have helped preserve them
. If I recall correctly it was especially good for removing encrustations from such coins. Does anyone know if there is any truth to this claim or, better yet, has anyone here ever used olive oil on their coins? Thanks.

 

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A few years ago I put a pile or slugs into a jar of olive oil. Let them soak for a few months and then gave them a good brushing - about half could at least be identified as to type (they were all LRBs).

I have a crusty sestertius in a jar of oil right now; hoping to see some improvement in the next year or so.

 

Kevin, A long time ago I posted a regrettable experience using olive oil to remove incrustation on a bronze follis of Diocletian . The olive oil along with a toothpick did the trick, but the slightly porous coin held an amount of oil that couldn't be removed ! On hot summer days oil would leech out onto the 2 X 2 flippet. I got rid of the coin to save my sanity .

 

I have used the olive oil soak method on late roman bronzes. It works well to soften dirt encrustations, and after soaking for a few months I was able to pull out the coins and using a toothpick and a dental pick I was able to clean some of them up, removing the dirt. So I had a beata tranquillitas type as well as a couple of gloria exercitus examples. What it does though is to impart a darker tone to the coin than it had previously, so that's one minor undesirable side-effect. Makes photographing them a bit tougher. Keep in mind that it doesn't work on the really hard encrustations that have become mineralized.

And whatever you do, don't use liquid descaler on lrbs. It completely destroyed a batch of 50 coins I had soaked for 24 hours. Sometimes people recommend this treatment for a quick fix as you can see the crud being lifted off the coins while they are soaking. But what you get is wholly uncollectible.

 

I just used a solution of white vinegar and salt to clean up some modern coins. It works really well with taking off fingerprints, surface dirt, smudges, etc. However, I would not recommend putting copper coins in the solution unless you don't mind them looking a little white. Otherwise, the other materials, including silver clean up nicely. Of course, you should never clean them unless they hold no "numismatic" value.

 

Olive oils works, because it contains acids. Acids are responsible for corrosion. Olive oil removes oxidation but remains in the pores of the material. It is only a matter of time before the coin falls to bits - Never use it. Severely corroded copper LRBs without value, can also be stripped with phosphoric acid (solution). The remnants of the acid can be removed in a simple process and if the surface of the clean (=stripped) coins is treated with christalline wax, they may live forever.

 

Olive oil seems to work for Popeye, if mixed thoroughly with spinach.

 

Sorry, but olive oil doesn't contain acids...olive oil IS an mixture of long chain fatty acids. They aren't very acidic, but the acid character perhaps adds to the stripping ability. Phosphoric acid is also very much an acid and I thought you were recommending removing the remnants with crystalline wax, but the removal would be with a base or something like baking soda solution. I wonder if soaking the olive oil cleaned coins in acetone or xylene would soak out all the oil.

 

AS the OP for this thread I guess I kind of expected mixed reviews on this. I did some research on the net and found the results there mirrored those here. it seems to be a mixed with bag with some reporting favorable and some unfavorable results. Though not a chemist, I am tempted to take some culls and try some experiments over a period of time to see what happens. Probably too many variables for anything more than an anecdotal observation or too but it might be instructive to attempt it. Anyone else tempted to try it?

 

It may be hard to come to any conclusion without waiting a very long time.

In general, this thread could use some ancient coins : I used olive oil soaks and a variety of brass brushes and scraping tools to clean AE coins ~20 years ago and I still have some of those coins - no evidence of any damage or disintegration 20 years later, but I wasn't working with priceless coins and I can't vouch for what this coin will look like in another 2000 years.

Maximianus Herculius, AD 286-305, Struck AD 295-299, Cyzicus, Radiate Æ
Obv: IMP C M A MAXIMIANVS P F AVG, radiate, draped, and cuirassed bust right
Rev: CONCORDIA MILITVM, Jupiter presents Victory on a globe to Maximianus, KE between
Ref: RIC 16b

Here's a very accessible web page on the chemistry of olive oil and there are certainly more technical analyses of fatty-acid/bronze interactions that would discourage use - I read this as: even if the olive oil might be fine, its degradation in the real world can cause damage:
Copper and Bronze in Art: Corrosion, Colorants, Conservation By David A. Scott

Renaissance wax probably a safer bet for preservation and cleaning.

 

Thanks for that informative response. Have you used this product or has anybody reading this used it on ancient bronze coins?

 

I recently bought a lot once cleaned with olive oil. There was some crud between the lettering and I tried to remove that mechanically under the microscope. The crud was very soft, but also the INSIDE of the coin. The thin layer of patina held things together! The inside was totally filled with oil which I tried to boil out in distilled water - with only little success.

 

I might question - which came first - porous coin or olive oil, but either way I'd draw the same conclusion: not recommended.

 

As I intimated in my post I no longer use olive oil. And in general I stay away from uncleaned coins, though it was a fun way to get back into the hobby.

 

You are absolutely right Kevin....Give Popeye spinach and he can do any/every thing! Even with his best friend Olive Oil!! Oh Yes....Yes he can.

 

I can't believe that in 2019 people still talk about olive oil. Back in 2004 I did this experiment with brand new pennies left soaking in olive oil for a couple of months.

Knowing this, would you still consider using it?
Rasiel

 

Question. Some of the coins look terrible. Some not so much. Why the difference?

 

As a slight aside, some people mention the porosity of some ancient coins. If you treated these coins with linseed oil, the oil should penetrate and then cure in place to give a plastic matrix holding the coin together.