An old thread from 2011, recently resurrected, called "PCGS Coin Sniffer" motivated me to do something I've been thinking about for some time. I have a number of early raw coppers ranging from little value to worth well into four figures. These are all kept in either mylar 2x2s, home slabs, and cotton envelopes and in humidity-controlled environments. Long-term practice among early copper collectors is to protect their coins with a thin film of mineral oil, applied gently with an extremely soft jewelers brush and reapply about every six months to a year. Looking at big-time early copper dealers' displays at the shows reveals pretty much all of their raw coins have the "shiny and wet" look that could be attributed to mineral oil or some other preservative. I've never done this but the talk in the afore-mentioned thread about PCGS having a sniffer that could detect mineral oil and some opinions that a mineral oil application constitutes an alteration of surfaces that is not market-acceptable prompted me to try it out. Now, I make no claims about market acceptability or whether or not a TPG would straight-grade a coin that has had mineral oil applied. I do not know. Nor do I make any claims to knowledge regarding Blue Ribbon, VertiCare or any other product. But I do know of some big-time early American copper collections that have gone to auction in straight-graded TPG slabs in recent years but that prior to auction resided raw in their owner's collections with mineral oil on them. So, below are some photos of a $5 large cent found in the junk box at my LCS. Obviously the subject of an earlier cleaning but otherwise pretty solid. Photos all taken within 30 minutes and with no change in lighting, exposure and no post-editing. First set shows the coin before any action was taken, the baseline if you will: Second set shows the coin post-cleaning which consisted of acetone baths and "Brakekleen" and final acetone rinse, air-dried. Final set shows the coin after a dab of oil has been applied with a q-tip (no rubbing) and spread with the makeup brush, then blotted with a soft paper towel. Since this was my first try, I put too much oil on the obverse but the reverse was just right. I have looked closely at this coin post-oiling both in my photos and at 30X under my stereo microscope and I see no hairlines whatsoever. Finally, a photo of the $3.95 mineral oil, pure with a bit of Vitamin E added as a stabilizer, and the $3 makeup brush from WalMart. You can be the judge of what you think of the aesthetic results but I think that for preservation, this is a pretty innocuous treatment. And it seems to me the oil treatment is 100% reversible since the mineral oil will just dissolve off in acetone. Your thoughts are welcome.
I am much in favor of the "after treatment" image. In fact you have motivated me... I had an ancient fashioned into a necklace for my wife years ago. Several years of being in contact with her neck have turned the coin dry and lifeless looking. I am going to try exactly your method on the old coin and see if it brings any life back.
I concur. Mineral oil is a great protective element to vintage bronze medals as well. Here are a few of mine that received the "treatment." Z
Personally, I like the look of the coin after the mineral oil was applied. It seems to enhance the surface and features, as well as protect the coin, and because it can removed easily with acetone, I see no reason not to do this to copper coins and tokens.
On a similar note... I actually have a question about collectors many years ago using grease... I still have a few authentic vintage wheat/indian rolls from an early days ebay seller. I have made some of my most amazing finds in these rolls over the years! A whole lot of the coins in these rolls that I've opened seem to have a fairly generous coating of mostly dried very very old grease or oil. Xylene and alcohol takes care of it nicely... But I'm wondering if any of you are familiar with this practice of greasing pennies? I've been opening rolls since the 70's...these are the only rolls I've ever had with the seemingly greased coins. I don't think it's an oil since none of the old wrappers have stains or indicate that there are many greasy coins in there. According to the seller, 20+ years ago, the rolls were made in the late 50's and early 60's by his Mom who worked at a bank for many years.
Thank you for sharing your copper/bronze conservation method. The finial result clearly shows a darker natural coin vs the pink coin you started with. I understand the mineral oil will preserve the surface but the coin looks oiled. Can the oiled look be toned down? Blotted with a soft cloth?
Absolutely, I agree. But that's not what I'm saying. Those raw coins that have been "oiled" and then went to the TPGs and got straight-graded must have had the oil removed prior to submission (that's my surmise, I can't prove it). And my point is that mineral oil is easy to remove while protecting the coin while still raw. Once the oil is removed, I very much doubt that the TPG's sniffer can detect its prior presence (again, I can't prove that but @BadThad's comments in the afore-mentioned thread supports that contention). I make no such assertions for any other product. My other raw early copper coins are going to be treated this way, including the 1793 half cent, maybe especially that one.
Yes, as I said in the OP, this was my first try at this and I put too much oil on. Because of that, even though I blotted it, I was hesitant to get too aggressive with the blotting. What happened was, I used a Q-Tip and allowed a big drop to fall off the Q-Tip onto the obverse surface of the coin and then gently wiped it into the surface with the dry makeup brush. When I saw that the application was too heavy, I just used the dampened brush to apply oil to the reverse. That was better but still a little too heavy. Lessons learned, that's why I used a junker to practice on.
Ah the moistened brush is key. I use a jewelers (horse hair) brush moistened with Classic Coin Conditioner. Excellent post BTW! The credit goes to this;
Yep, Bill knows his stuff! BTW, I could not find a jeweler's brush like Bill uses in the video despite looking all over the internet. I used to see ads for them in Penny-Wise (the EAC journal) but not for a long time.
Amazon has horsehair brushes for watercolor artists. Not the best for watercolors, but cheaper than sable or such. Jim
Mineral oil is good for giving some "life" to duller copper surfaces, but hard to avoid the wet look. Petroleum jelly is essentially the same, just a more solidified version that should last somewhat longer. With either of these hydrocarbon treatments, I would be concerned that the chemicals would fog the interior of the coin capsule or flip that the coin is in. Since the coins to be treated are free of grit (hopefully) a gentle rub with a soft cloth would remove more of the oil and lead to a better appearance IMHO.
