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.