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Treating copper coins with oil...
dan1ecu
Posts: 1,573
I’ve heard of the practice of coating copper coins with oil to give them a glossy appearance. How common is this? I assume that the grading services wouldn’t slab such a coin unless the oil was removed. Would a coat of oil guard against corrosion?
Dan
Dan
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oil-hydrochloroflourocarbon mixtures, like the old "Blue Ribbon" are recommended by many, but others say don't use them, especially on Mint state coins. Not an easy question to answer.
Yes. I recommend 30 weight. Just kidding
It is to be used essentially for full or near full red BU copper coins to keep them that way. Not to be used on proofs for obvious reasons.
I have used such mineral oil for over 33 years now. PCGS has never had a problem with any of them once the oil was dried off the surface.
Do a search of mineral oil or just oil in prior numerous threads on this topic.
Use of "Blue Ribbon" on BU coins will turn them non-BU very quickly. It gives them an unnatural tinge. If you use it on circulated copper them follow it up with pure mineral oil, you're somewhat safe.
Pure mineral oil, the kind you can drink for regularity (you get it at the drug store), is the only - ONLY - kind of oil you can safely use on BU copper. Motor oil, machine oil, gun oil, Bule Ribbon, olive oil, and vegetable oil all either rot over time, change the color of the coin, or will corrode, thus corroding the coin. The pure mineral oil is the only one I know of that will not do any of this and is completely safe.
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K S
Obscurum per obscurius
No, definitely not! Mineral oil is only a protectant. Sadly, most green corrosion spots are verdigris, which has already chemically interacted with the copper, you can use other means to remove the green, but the coin will be pitted in most cases.
Of course, you have to check on the oil in the holder to make sure it does not evaporate. I use the hard 2x2 plastic holders (the nickel sized ones) and they generally do not evaporate more than every three years since I seal them tight in a plastic (non PVC) bag.
dorkcarl: When one is finished with the mineral, it is dried off by squeezing the oil off the coin against a soft cloth lined with soft tissue paper. No evidence of oil remains. The coins then tones no faster than if it had been left alone in the first place. All the oil does is to keep the air out/off the surface of the coin to prevent toning. Period.
K S
I followed the suggestion using olive oil and it worked great.The coin came to life and looks like respectable. Twowood
In fact, I dislike glossy circulated copper coins. I never understood why they should sell for a premium unless in AU or better condition or in the case of a proof copper coin.
However, in the case of a strictly uncirculated and lustrous coin that is full red or very close to full red, mineral oil has been marvelous for the past 50 plus years. MIneral oil has no dealers touting it since there is nothing to sell or hype.
Intercept has been too new to see how long it will last as there is no indicator on such holder to know how long the life expectancy of such intercept holder is. At least with mineral oil, I can see exactly how long the mineral oil is working for, in the case of when it begins to evaporate.
Also on lustrous BU copper coins mineral oil does NOT make the copper coins look glossy since the original luster is NOT affected in any way, positive or negative. It is completely inert and only serves to block the harmful air out.
<< <i>dorkkarl: I believe you are speaking of circulated copper coinage and their glossiness. >>
that is correct, thanks for bringing up that point.
<< <i>In fact, I dislike glossy circulated copper coins. I never understood why they should sell for a premium unless in AU or better condition or in the case of a proof copper coin. >>
i can't disagree, except that the glossiness provides a more "accesible" surface for minute examination in determining die states, planchet quality & striking phenomena. regrettably, it is often the case that only examples in low grade are available for such study
K S
K S
Blue ribbon did wonders for an early half cent with extremely streaky planchet I have, but color looks somewhat unnatural... and now that I know what to look for, can spot them a mile away.
Note that I'm not slathering the Vaseline on in huge amounts and leaving it there- I apply it and remove it, with a soft cloth or paper towel. To prevent buildup in the lettering and other detailed areas of the coin, the Vaseline can be removed from those areas with a cotton swab ("Q-tip"), if necessary, but I usually find it isn't. You should see the cloth after I have used it to wipe the Vaseline off- even if the coin was pretty clean-looking to begin with, the Vaseline is almost always greenish-brown when it comes off the coin (the particular cloths I use are white, so it shows up well- you'd be amazed what's been sitting unseen on the surface of a lot of your coppers!)
Oils often dry up leave a greasy or sticky residue. In my experience, a coin that's been Vaselined and then had the Vaseline removed will be glossy and yet not overly greasy. Note also that I do not use the Vaseline on proof coins or most Mint State pieces. It might be usable on red copper pieces, but I do not recommend this as I have never tried it- I pretty much just use it on circulated stuff.
Collector since 1976. On the CU forums here since 2001.
Also I do not have to "wipe" mineral oil off from the coin. Isn't wiping off the vaseline from the coin going to leave wipe marks?
I also find the vaseline more messy to work with.
If you use it on circulated copper to remove dirt or gunk, after the treatment, YOU MUST REMOVE IT!.
It will change the color of copper, especially in areas where wear is apparent.
I used Blue Ribbon to clean a common date Lincoln to test how it works.
It did a beautiful job removing caked up gunk. It also turned the areas with circulation rub a wierd looking off color reddish tone.
So I tried it again on another coin...this time after I treated the coin, I ran it under warm water and applied dishwashing liquid to both sides. I rubbed it with my fingers till it soaped up, then I rinsed it.
I put the coin on a paper towel and pressed the towel (no rubbing) on the coin to dry.
It worked. It took off the sheen, the coin looks natural, and the coin has not changed color.
I'm not telling you to do what I did. But, if you must fool around......run the same test I did and see for yourself.
Pete
Collector since 1976. On the CU forums here since 2001.