Citric Acid in Coin Conservation

I was watching The Curse of Oak Island the other day and they took a coin that hey had found to a "treasure expert". They proceeded to show him cleaning the oxidation off the coin with citric acid. See clip below:



This got me thinking... If this guy works for a treasure salvage company, what does he know about citric acid and coins that I don't know?? So I decided to try some experiments.

When it comes to treasure salvaged coins and "conservation" there is a different ballpark of what is acceptable. Often these treasure coins have been exposed to prolonged periods in a saltwater environment and without harsher forms of cleaning they would eventually disintegrate.

I had a 1907 Philippine one silver peso that had a spot of oxidation on the wing... this is most likely a result of exposure to seawater. I mixed a light solution of citric acid and dropped the coin in. You can see that the oxidation on the silver is the only thing the acid is touching and is not effecting the clean silver at all.




I'm doing some further experimentation I'll report here what I find.

I DON'T RECOMMEND EXPOSING ANY OF YOUR COINS TO ACID. DON'T DO IT!

 

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That's unfortunate. It basically shows the treasure expert cleaning the copper coin in "mild" citric acid.

 

Here...try this:
http://www.history.com/shows/the-cu...sh-coin?m=5189719baf036&s=All&f=1&free=false#

 

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Us ancient collectors do it every so often to get rid of some of the harder copper deposits. Mostly with the silvers. Works wonders most of the time.

 

Speaking of chemical cleaning, anyone ever try oxalic acid?

 

It worked for me.

BTW, I am not sure what you mean by "mild", but that bottle said 50%. And this may be why they use it;

 

I was wondering the same thing when I saw the show. Let me know how it turns out, sure would like to clean up some of my Katrina coins.

 

Because you are in the US

 

Citric acid is much weaker than so-called "mineral acids" like nitric, hydrochloric or sulfuric. 50% citric acid would be a lot less corrosive than diluted hydrochloric acid; in fact, it might well be less corrosive than vinegar, which is 5% acetic acid, itself not that strong.

 

Yes, I know that.

 

Quick chemistry course. An acid is anything that supplies a hydrogen ion in water solution. Hydrogen ions are notorious for attacking certain metals (zinc, iron, etc) and dissolvinmg them. They also attack organic matter (crud on a coin) and sometimes can attack materials causinmg corrosion to the coin. An acid is strong if it breaks 100% into hydrogen ions in solution or weak if it doesn't. Strong acids are hydrochloric, nitric, sulfuric and perchloric. Pretty much everything else is weak.

 

Never on coins but it works wonders to get stains especially black iron based ones out of wood

 

To bad I don't have a bunch of real crappy crusty junk silver I could experiment with I have many products I use on furniture restoration that may work

 

Yes I have but not on coins. Boiling quartz rocks in Oxalic can bleach the rocks nicely. Here is the biggest piece of quartz that I have boiled in oxalic:

 

Maybe I'll order some and give it a tinkering with...

 

If you boil with oxalic, do it outside on a hot plate or grill that you intend to throw away. It dissolves stuff (like your lungs if you are not careful). I was making the point that it is used on ROCKS. It is not necessarily good for coins or humans.

 

I don't plan to boil it... Just dissolve in hot water and see what it does. I have a bunch of ground found brown buffalo nickels I want to see what it does.