What is the proper way to conserve a copper coin?

[dleonard-3]

I've always heard that you should never "clean" a coin, or you will ruin it's collector value.  However, I have also heard of conserving or curating a coin, which isn't considered "cleaning", but simply maintaining and preserving the coin.  The technique is simply to gently remove any debris and gunk which would eventually cause oxidation and corrosion, and apply a very light coat of an inert preservative/protectant.  A clean soft bristle jewelers brush is used to apply the protectant.  I have tried this on several of my Large Cents, with excellent results.  But I would like to discuss proper procedures, as well as any negative effects this might have on the value of my coins.

[Six Mile Rick]

NCS conservation.

That 1856 looks nice. I like them dipped in chocolate!!

[physics-fan3.14]

The way you approach conserving a coin depends on what's wrong with it. 

If it is heavily encrusted and porous from long term environmental exposure, you're going to want to remove the crud and stabilize the surfaces. 

If it has verdigris, you'll want to use Verdi-Care, a formula invented by a chemist on CoinTalk known as BadThad. It is quite successful in reversing the chemical reactions. 

If it has PVC, you'll want to use acetone. 

Sometimes, NCS is the last resort and should be used, but it is expensive for lower valued coins. 

The more damage that has occurred, or the stronger the method you use to conserve a coin, the more it will affect the value. As long as there was no permanent underlying damage, something like acetone removal of residue will have no affect on the value.