The First Steps to Proper Coin Conservation

[Vickilynn]

What is Verdi-care ? Vickilynn

[heavencent]

This is such valuable information. I am afraid I have ruined some coins, but not anymore. Thank you.

[BadThad]

Thad, some dealers have suggested using Olive Oil. Just curious on your opinions of that.

I am strongly against using any oil on coins (vegetable or petroleum) for many reasons. Here's the OO section from the book I'm working on (sorry, no pics though)....I'm willing to share it with the community because I think it's important.

As a result of its popularity, I have devoted a large section of this book to olive oil in order to help the layman understand how it works. Olive oil has been a long time favorite of collectors for the conservation of coins. You will read everywhere people recommending its use to remove coin surface contaminants. If used carefully, it has many advantages and I’ve seen collectors successfully conserve coins using EVO. On the flip side, I’ve also seen collectors damage their coins using it. The main problem with EVO is consistency from bottle to bottle. Since it is a natural product, the contents can vary greatly from batch to batch. EVO is made for eating and not for chemistry!

EVO is a mixture of many chemicals, mainly triglyceride which is three fatty acids attached to the glycerol molecule. Oleic acid (CH3(CH2)7CH=CH(CH2)7COOH) is present in high amounts in EVO, perhaps 50% or greater. Also present are Linoleic acid (< 10%) and Linolenic acid. There is also a small percentage of water. Being a natural product, it also contains other fatty acids, volatile organic compounds, vitamins, water- and oil-soluble organics compounds and finely ground olive. It’s quite a mixture! Here’s what some of the molecules look like in chemist speak:


Before we continue there are a couple terms that need to be defined for the layman:

Lipophilic – Oil loving, molecules that tend to dissolve in oil are lipophilic.
Hydrophilic – Water loving, molecules that tend to dissolve in water are hydrophilic.
Proton – Hydrogen ion, Hydronium ion, H+ are all the same thing. Chemists like to keep you confused!

As far as verdigris removal with EVO, the primary mechanism is a reaction between the fatty acids and copper salts. Acids will release a proton (hydrogen ion) in solution. This is what makes the solution acidic. That proton is highly reactive and it will easily displace the copper salt anion through reduction. For example:


Copper Acetate + Hydrogen Ion à Acetic Acid + Copper Ion

This reaction will occur with all of the copper salts previously discussed. As we can see, copper has been reduced, the verdigris component has been removed and solubilized as an acid. Another interesting reaction that seems to appear when using olive oil is the appearance of a subdued red patch under the verdigris. That red patch is a very thick layer of copper oxide (cuprous oxide).

It is important to note that we now have corrosive acetic acid in solution. As long as the solution remains acidic enough, the reaction will continue to drive toward the formation of acid. Unfortunately, the acid will also aid in the attack of the metallic coin surface. Given enough time, surface damage will occur.

There are a couple primary chemical mechanisms at work when you soak a coin in EVO.

1) Oil solvency (lipophilic property) – Oil is a solvent. It has the ability to dissolve “like” materials. This is the basic chemistry principle of “like dissolves like”. In its case, long-chain organic molecules (lipophilic molecules) will tend to move from the coin surface into the EVO solution. With respect to verdigris, the oil solvency factor will have very little effect because most of the verdigris composition is inorganic (no carbon atoms). Inorganic (no carbon) materials are hydrophilic and not lipophilic. To some degree, EVO will dissolve any unbonded acetate free radicals and bring them into solution due to the slightly lipophilic character of acetate.
2) Organic Acids – EVO contains organic acid molecules. As discussed above, those lipophilic organic acids are proton donors which serve to break the ionic bond of the copper salts.

The problems with using EVO are many fold:

• The acid-verdigris reaction process proceeds very slowly. The mobility of the free protons in an oil solution is very low. Just imagine if you dropped cork balls into a jar of water and into a jar of oil and then shook them side-by-side. In the water solution the ball would rapidly more around as you shook it. It the oil solution the ball would barely be moving as you shook it. This is why it can take months of soaking even a lightly infected verdigris coin in EVO before results are seen.
• EVO is natural so it degrades and goes rancid. Over a period of time the oil will oxidize and spoil as bacteria eat away at it and grow. It must be replaced frequently with fresh oil or the spoiled EVO may cause harm to the coin surface. The complex organic degradation products could prove to be quite harmful.
• The chemical composition and acids levels are inconsistent. Being a natural product, there is a lot of variation in the acidity, ingredients and contaminants. A bottle that has worked for the conservation of one coin may not be exactly the same in the next bottle.
• Acids are very corrosive to copper and the oil will solubilize some of the natural brown patina that has developed on a copper coin. Working together, both of these mechanisms may alter the coins appearance and may even permanently destroy the surface by pitting it.
• Once you apply any oil to a coin the only way to remove it is to use a non-polar solvent like xylene. Even then, you won't get full removal on a coin with corrosion because the oil and its impurities tend to get deep down into the corrosion. These impurities can actually act to accelerate the corrosion process and add to the damage. Assuming the oil doesn't produce the desired results (which it rarely does), you're now forced into using more/different treatments on the coin. A rule of thumb for successful conservation is LESS IS BETTER. The more things you try, the greater the chances you'll permanently damage your coin.

[BadThad]

Brad, I know you want Thad's opinion on this, but I had the same question before. I was told that olive oil is also acidic. Therefore it would not be good for the coin. The person I heard this from said he would only use olive oil on a dug coin that had no hope at all.

On a side note Thad knows I am one of his biggest fan's. I keep a good supply of Verdi-care on hand. Folks this stuff is THE BEST product I have ever used. Hands down.

Olive oil on dug coins is fine, it usually does a decent job because it's so harsh. With dug coins you've got basically nothing to lose. You either have a chunk of crapola or a coin you can read.




...and thanks for the kind words!

[ShyCent]

Wonderful, Thad. This whole thread is a top 10.

[SDP73]

I am strongly against using any oil on coins (vegetable or petroleum) for many reasons. Here's the OO section from the book I'm working on (sorry, no pics though)....I'm willing to share it with the community because I think it's important.

Any updates on the book? You can go ahead and put me down for a copy.

P.S. My Verdi-Care is on the way from Wizard as we speak...should be here tomorrow or Monday.

[BadThad]

Any updates on the book? You can go ahead and put me down for a copy.

P.S. My Verdi-Care is on the way from Wizard as we speak...should be here tomorrow or Monday.

No time to properly devote to it. I wrote most of it when I was laid-off in 2009. Kept the chemistry working in my brain.

Not sure when I'll get around to it again....someday. Next time you want some VC, drop me a PM. I offer a discount to LCR members.

[SDP73]

No time to properly devote to it. I wrote most of it when I was laid-off in 2009. Kept the chemistry working in my brain.

Not sure when I'll get around to it again....someday. Next time you want some VC, drop me a PM. I offer a discount to LCR members.

Will do. Thanks! Im excited for it to get here.

[busyeye]

Been following your counsel and direction since I got the Verdi over a year ago. This post, is educational, important and good reminder.

Thank you!

[jhcons]

This thread needs to be somewhere 0n this site where people can view it along with some others that is just information that is needed to know.
Jim