The Numismatic Guaranty Corporation (NGC) has created several videos on their
NGCCoinVideos YouTube channel. One that I find especially interesting is the NCS Conservation Video. Numismatic Conservation Services (NCS) is a sister company of NGC. As stated on their video:
“NCS provides expert professional conservation services for public and private collections of coins, tokens and medals. Coin conservation can help remove harmful residues and stabilize the surface of your coin”
This video features amazing before and after pictures of coins that have been conserved by NCS. Not all coins benefit from conservation, including those with active Polyvinyl Chloride (PVC) residue. PVC in some coin holders can react with the surface of a coin and leave a “green slime” or haze. As stated in the video, some Chinese modern coins acquired a haze from their shipping holders. If the conservator determines that the PVC is inactive, the coin’s original surface may be restored. Blemishes like copper spots can also be removed.
Conservation may be an opportunity to restore eye appeal and add value to previously undesirable coins.
Disclaimer: I am not affiliated with NGC or NCS although I have had a few coins certified by NGC.