Rightly or wrongly, I only ever wipe/pat(Peter) off as much as I can to make the coin dry in appearance again. I never remove ALL the oil residue with something else, like acetone for example. Copper/brass coins always look beautiful after a wipe of oil, almost conditioned but, I have asked the question on here many times, whether anyone has ever noticed any long-term effects from exposure to Olive Oil. I think I recall Peck saying that he hadn't noticed any changes, in around 80-90 years of observing I think it was (don't quote me on that, it might be longer) Am I going to get hate mail for this, but I routinely acetone and oil my copper coins before sealing them up in 2x2's. I've been doing that for around 4 years and haven't noticed any changes yet.