OK To Use Mineral Oil As A Protective Coating?

leave the coins alone

It was considered normal many decades ago to give coins a protective layer of oil. It worked surprisingly well, and many of the stunning coins of today only look like they do because they were well-preserved in oil. But this practice is frowned on today, for two reasons:

- Who knows what's in the oil - there might be compounds in there that do more harm than good to a coin. Certainly oil does little or nothing to preserve lustre, and may even hasten it's disappearance.

- Modern coin storage methods appear to do a much better job at protecting coins than the old-fashioned oil layer method.

Of course, it's always possible that people in several hundred years time will be cursing our generation for using coin storage and preservation methods which will do more long-term harm than good, too, just as we tut-tut previous generations that used oil or PVC plastic.

I could maybe see doing it with old copper that has had previous corrosion issues as a way to keep the corrosion in check. Oiling or laquering copper used to be common preservation practices- remember that large cents and Half Cents were pure copper, not an alloy. However, I do not see a purpose in doing that to coins of other compositions or even copper coins with relatively pristine surfaces.

Biokemist, yes--my largest collection is bronze/copper coins from the 19th-20th C so that's what I'm thinking about here.
As any corrosion tends to draw in moisture, a surface trace of oil might impede that process.
Of course, the best protection for any copper coins is storing them well in the first place.
I don't do this for MS or otherwise "pristine" copper coins, but otherwise I'm satisfied that pure mineral oil* won't harm my coins.
But--every collector should check this for themselves.

*I have used "food grade pure petrolatum mineral oil"

How would you ever get the oil off in the even that you wanted to completely remove it? would the solvent that you would have to use damage the coin? You could end up with a perfectly preserved oily coin, that wouls forever be coated in oil...

Those solvent won't do a good job at removal of oil, they are too polar in nature. A much, much better choice would be xylene or toluene, both are miscible with oil.

On the subject of coating coins with oil. I would never take that approach since today we have things like airtites and Intercept Shields.

The best thing to do is use a very high grade of rear axel grease. Not the white stuff, but that nice, black, thick stuff also used to grease most cars front ends. I would guarantee those coins will still look the same in a few hundred years too. Other such great methods of preservation are liquid plastic.
For real though remember that any substance that has a sticky or slimy residue will attract dust and dirt. This means such items placed on a coin will eventually make the thing a really big mess. Of course if placed in an air tight container after treating with any oils, not much dirt will get to the coins. Of coures if the coins are placed in such containers, no oils would have been required.

^ I think i'd rather see my coins age, with grace :)