PVC spot 'growing' in NGC holder

[HillbillyJim-migration]

Hello... I've had this coin about 2 years & have noted a small blue/green spot near the rim that has grown a little larger to about the size of a match head. The coin is a brilliant NGC MS-67 BTW .

 

What is my best course of action to have this problem resolved? I'm 99% sure it's PVC & of course will have to crack the slab to remove the spot.

 

Many thanks, Jimmy

[Guest]

PVC is nasty problem and can be virtually invisible but as it decays it releases Hydrogen Sulfide that can damage and discolor the coin. I wouldn't try to remove it without expert help. Contac NGC' about their conservation services for help with this problem.

 

Stancolor=green>

[TomB]

Post deleted by SKlein

[Guest]

There are two issues with PolyvinylChloride holders:

 

• Softener agent - this keeps the flip flexible. When the PVC holder decays the softener (plastisizer) decays. This is the oil residue that coats the surface of a PVC exposed coin.
• When the PVC chemically breaks down it releases Hydrogen Sulfide gas which combines chemically with the coin's surface. The resulting chemical combination depends on the existing oxide coating that is already on the coin. This explains why some coins are damaged by PVC breakdown where others just suffer from being coated with oily residue.
• An chemical example of a copper coin rapidly tarnished by being subject to Hydrogen Sulfide is:
  Cu + H2s = CuS + H2
  copper + Hydrogen Sulfide = Copper Sulfide + Hydrogen
  

Note that 3 to 5% solution of hyrdochloric acid is one of the many methods that are used by conservators for removing encrusted soil and other residue from coins, especially ones found underground in archeological digs. Please don't try this at home

[TomB]

I guess the problem I am having with accepting that PVC liberates hydrogen sulfide is the concept of where the sulfer is coming from. Since PVC itself contains no sulfer (this is true, isn't it?) then it would need to react with something else in the environment to form hydrogen sulfide.

[Guest]

PVC is bonded chemically to the plastic to make it soft. The problem comes when the chemical combination comes apart. this can occur due to heat or age and can happen rapidly or slowly.

 

There are plastic flips that are sold without PVC but they are rather brittle and can scratch coins. Mylar flips are the most stable.