Why olive oil???

[Cubfan64]

I want to start doing some investigation as to why olive oil seems to be able to clean some older coins and thought this might be a good place to start talking about it.

What types of coins do people recommend be cleaned this way, and which ones are not recommended (and why).

What kinds of before and after pictures do people have from olive oil cleaning?

What are the theories as to how and why olive oil works (as opposed to motor oil, corn oil, etc...)

Anyone have bad experiences using olive oil?

Being a chemist by education and trade, I'm just very curious as to what exactly olive oil specifically does to clean coins. Could it be that it just started as an old wives tale and evolved into "the right" thing to use? Maybe any kind of oil would do the same thing? Maybe the olive oil method could be improved upon if we knew exactly why it seemed to work?

Any insight any of you could give would be wonderful - I'd like this thread to develop into a learning tool for me to get information from those of you who have tried using it and either had success or failure and try to get specific so I can understand what's happening.

Thanks

 

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[Don in SJ]

Well, I will respond since I am an advocate of not using Olive Oil......

What types of coins do people recommend be cleaned this way, and which ones are not recommended (and why).

Most use it on copper/brass/bronze. Not Silver or clad.


Anyone have bad experiences using olive oil?

Yes, I used Olive oil for cleaning buttons, and my copper coins for almost twenty years, and I have a couple hundred or so Mylar folders that show how the oil in the ground found coppers had permeated and leached back out onto the folders. The coppers get darker, and a button, oh my, if it is a two piece or a blowhole type, will have oil leaching out for years.

I started using Olive Oil back in the early 80's because that is what others were doing (before internet days by the way) I never was happy with how long it took on some coins, and still did not do a great job.

Olive oil is acidic and to think a copper is permeated with it, means the acid is then trapped in the coin, which most likely does not help maintain a long survival rate...

About 6 years ago, some posted about trying Hydrogen Peroxide on coppers and buttons, and I did, and have not looked back.

There are die hard Olive Oil fans out there, and that is fine, but I will never use it again.

The procedures I use for cleaning buttons and coppers are further down in this forum.

Don in SJ

 

[Cubfan64]

Well, I will respond since I am an advocate of not using Olive Oil......

What types of coins do people recommend be cleaned this way, and which ones are not recommended (and why).

Most use it on copper/brass/bronze. Not Silver or clad.


Anyone have bad experiences using olive oil?

Yes, I used Olive oil for cleaning buttons, and my copper coins for almost twenty years, and I have a couple hundred or so Mylar folders that show how the oil in the ground found coppers had permeated and leached back out onto the folders. The coppers get darker, and a button, oh my, if it is a two piece or a blowhole type, will have oil leaching out for years.

I started using Olive Oil back in the early 80's because that is what others were doing (before internet days by the way) I never was happy with how long it took on some coins, and still did not do a great job.

Olive oil is acidic and to think a copper is permeated with it, means the acid is then trapped in the coin, which most likely does not help maintain a long survival rate...

About 6 years ago, some posted about trying Hydrogen Peroxide on coppers and buttons, and I did, and have not looked back.

There are die hard Olive Oil fans out there, and that is fine, but I will never use it again.

The procedures I use for cleaning buttons and coppers are further down in this forum.

Don in SJ

Interesting - so do you think it's the acidity in the oil that's the only thing really "cleaning" the coin?

I can definitely see where any porosity in an object would allow even minute amounts of oil in which would certainly leach back out over time. Since oil is soluble in a variety of solvents (degreasers like methylene chloride and others), I wonder what would happen if you soaked the coin in solvent after the oil treatment - theoretically over time it should leach out the oil.

Does olive oil actually "eat" off the outer layer of grime, or do you think it just permeates through to the coin turning everything not solid metal into "mush" that can be cleaned off eventually - hopefully leaving whatever remains of solid coin behind.

I know this probably isn't interesting to alot of you, but I appreciate the feedback.

 

[Don in SJ]

I think olive oil mostly works just by the fact the object is soaked so long in an "oil" that it does just evenutally loosen, or as you said turn the grime to mush. Maybe a mineral oil would work the same, I just do not know and just know I am done with that method.

I am sure others eventually will voice an opinion or two. Don't get me wrong, the olive oil does clean to some degree, but so does just about anything else. The trick is to clean without destroying or as I stated destroying over a long period of time from the amount that was absorbed into the item...

One of the most important things that must be done for long term preservation is the absence of moisture of any type, a coin or button must be throughly dry for display in a folder, including no oil.

Don

 

[FMarion2ndRegSC]

I'll add my experience here (which of course is totally different from expertise...something I don't profess). I find alot of my relics diving. I target Rev War/colonial sites, typically. I found many years ago that water found pewter buttons when they dry out, tend to crack and become very brittle in general. I find that keeping them wet until I get them home, then patting them dry before immersing in olive oil, greatly reduces this process. Again, not being a metallurgist or otherwise, I have assumed the porosity of the pewter allows the oil to replace the water avoiding the evaporation of the water which I believe causes the cracking, flaking of the pewter. I know your question specificlly addresses coins. Olive oil works beautifully on silver coins with a "skin" of silver oxide/grit that occurs on the water found coins. It appears as a "skin" similar to powdercoating. The oil permeates the layer and separates the skin from the silver, whereby it is easily flaked off with toothpicks. They do not seem to form this skin if they are found in shifting sands. I'll also second the "turn the crud to mush" theory, as I have utilized this method repeatedly with good results. Here is a good example. The first pic is a pewter Rev War button and reale before any cleaning save lightly brushed under running water. You can see small areas on the coin where the skin has flaked off, but the rest was tenaciously adhered. The second pic is the button after soaking in olive oil 3 days and clean away the "mush". The third pic is the reale after soaking 3 days...the skin flaked off very easily with toothpicks avoiding any scratching to the underlying silver face. Of course, if I found an extremely valuable coin, I would leave the cleaning to a numismatic. I have mixed results on copper. I think the bond between the crud and the copper is chemically different and much more tenacious. Just my thoughts.

 

[Don in SJ]

I know a few of the top button collectors and especially one of the top Rev War button collectors and he told me for pewter buttons, either use wax or spray lacquer, never an oil of any type.

True, your olive oil will, stop the flaking of the button, since you are preventing it from drying out, but also long range destruction is taking place and as I stated earlier the oil will start and continue to leach out slowly for many years to come.

Best to seal to preserve...



Don

 

[FMarion2ndRegSC]

I respect your info, but my problem with the water found buttons has always been the initial dehydration. Laquer would just seal the moisture in just delaying or even prolonging the degradation. I have heard of the wax sealing method, but again that doesn't solve the initial dehydration problem. Do you know if they have any solution for this? Once the dehydration occurs the damage appears to be done. The oil leaching out over many years doesn't seem to be a problem with my pewter buttons that were water found and if anything prevent continued surface corrosion. I acquired a button of the 30th regiment from THE expert on Rev War buttons that was water found and the surface is bubbled, but since the damage is done, I, of course, didn't treat it with olive oil. Do you know what the exact nature of the destruction to the pewter is?

 

[Don in SJ]

I sent an email to my Rev War button collector friend asking his advice on your question for the water found Pewters......Hopefully a good answer will be given and of course I will pass on what he says.



Don

 

[Don in SJ]

OK, here is the reply I received from a Rev War button collector.

I've never used anything other than silk-finish spray acrylic to seal excavated pewter buttons. Some of these were dug up to 40 years ago, and not one has ever developed problems. Thus, I have no familiarity with olive oil but the entire idea sounds highly incorrect.

IMO, the major problem with excavated pewter buttons is "layering." That is, the outer surface of the metal begins to loosen and separate from the main portion. That's what has happened to buttons with "rim chipping" or those that have lost the sharpness of the detail of the device on the face; the outer surfaces have pulled away. Thus, I'd have a big problem with any lubricant, whether olive oil or any other oil. Such lubrication, logically, would add to the likelihood of such separation results, not reduce it.

From what I've read on the forums, it seems that the guys using olive oil are almost undoubtedly working with brass buttons, not pewter. Also, I interpret that their goal is to remove adhesions from the brass, i.e., separate or pull away the residue. The latter is rarely the case with pewter buttons. The surface soil will rinse off, but if the pewter is otherwise stained, it's more likely than not that the stain has penetrated the surface (due to pewter being far more porous than brass.) If one tries to "soak out" such stains from a dug 18th-century button, I believe that's a self-defeating goal. Once penetrating stains have occurred, it's more likely that the top layer of pewter will end up being removed.

I'll stick with rinsing, thorough drying, and sealing against future oxidation with a very light coating of spray acrylic.

My friend has quite an extensive collection of Rev War buttons and I would consider his advice, expert advice, since he is a long time collector and buyer......

Don

 

[FMarion2ndRegSC]

Thanks Don for your efforts. I think this subject needs much more research. Your friend having buttons that have seen no ill-effects after 40 some-odd years post-preservation certainly lends support to his current methods. If I understand correctly, he is a proponent of removing only the loosest of debris and then sealing the remaining corroded layer/debris down with acrylic, thus retaining the most detail possible, while hoping to prevent further corrosion from occuring. Does that sound correct? I still have an issue concerning the problem of initial dehydration. I have seen beautifully perfect,pewter Rev War buttons come out of the water with perfect edges and raised devices and by the time I got them home and they dried out, edge cracking had already begun to occur. I have prevented this by simply keeping the button wet and then soaking in olive oil. I'm not sure spray acrylic would adhere to a moist button, and, in such a case, am concerned that if any separation of the acrylic and metal ever occured it could be a disaster. It certainly seems among collectors that prevention of further corrosion by reducing exposure to oxygen is the common goal. I'm convinced that acrylic is an effective stabilizing method, long term, but a little concerned with it's irreversibility and color stability (I've seen clear acrylics tend to yellow over time depending on exposure to sunlight or atmospheric changes). I guess,ultimately, my rationale has always been that for centuries corrosion has been effectively prevented on metals of all kinds (guns, swords, machinery) using oils. Olive oil, with the added benefit of being a fairly benign cleaning/loosening agent not frowned upon by numismatics, is my preservative of choice, particularly on the water found pewter buttons until I see something scientific that will convince me otherwise. Thanks again ( if he's been collecting 40+ years, I would love to see your friends collection in person !!!)