PVC and Acetone - Part 1 of a 3 Part Series: PVC

[physics-fan3.14]

There have been quite a few questions recently about acetone and PVC, so I think its time to repost this. I covered some of this information in a thread a few years ago, but this is a greatly revised and expanded version. This will be Part 1 of a 3 part series – part 1 covers PVC (the problem), part 2 will cover the science of acetone (the solution), and the final part will be a detailed step by step pictorial guide to conserving your coins with acetone, so stay tuned. Before we begin, let me just tell you what I am trying to do with this series of threads. There are so many myths concerning acetone, and what it does to coins, and how to use it, that I feel the need to clear some of them up. By examining the science of a subject, you gain a deeper understanding of it – why and how something works takes away the mystery of it. I am hoping that this series of three threads can be a compendium of knowledge on PVC and Acetone, and that it will be useful as a reference when answering questions.

 

So many collectors have left their collections or their hoards for years, only to discover when they look at them again that there is a green slime covering their coins. If he is lucky, this slime can be removed and the coin underneath is fine, but if he is unlucky, permanent and irreversible damage as this goo has eaten into the surface of the coin. An ounce of prevention is worth a pound of cure, as the saying goes. I hope that none of you ever experience this, but just in case, and in the event that you are unsure, I urge you to examine your flips, holders, cases, and storage after reading this thread. This green goo has a name, and its name is PVC.

 

PVC, or Poly Vinyl Chloride, is a plasticizer used to soften plastics and make them more pliable, and its chemical formula is

 

(from Wikipedia)

 

The brackets just mean that it is a continuing chain, hence the poly - a polymer is made up of individual molecules that have undergone polymerization, that is, they have become linked together to form a chain that can be extremely long. Some polymers have individual molecules that weigh many grams or even kilograms. PVC is a simple polymer, based on your standard hydrocarbon: one of the hydrogen atoms has been replaced with a chlorine atom.

 

PVC was first made (accidentally, like so many other useful things) by a German chemist in 1912. His company patented it, but had no idea what to do with it. It wasn't until after their patent ran out that a chemist at BF Goodrich independently discovered PVC in 1926, and came up with the idea to make shower curtains out of it.

 

PVC is bad for coins because over time as it breaks down, it releases hydrochloric acid which eats into the surface of the coins. Hydrochloric acid is very dangerous, yet essential to life as it is the acid in our stomachs which dissolves food (if mixed with bleach, it also produces deadly chlorine gas). PVC was first made by reacting acetylene with hydrochloric acid, so it only makes sense that HCl could come back out from it. PVC residue will manifest as a green, or sometimes brown, film or buildup on the surface of the coin. You can usually tell it is PVC by smelling the coin: if it smells like a shower curtain, you can be certain that there is PVC present. If your coin is affected by PVC, don't immediately panic. It takes some time for the PVC to do irreversible damage to a coin. An acetone bath will dissolve any PVC residue (and will be discussed in great detail in part 2 of this series). If it hasn't eaten too far into the surface of the coin, it should be indistinguishable from an unaffected specimen. The green color is due primarily to the copper present in all silver alloys. The hydrochloric acid leeched from the PVC reacts with the copper in the alloy and forms copper chloride, which is has a bluish green tint. The copper chloride is also one of the components of verdigris, a common ailment on copper coins.

 

(A teaser for part 3: see the coin this flip contained, and what happened to it)

 

Another important consequence of using PVC flips is that the surfaces can become impregnated with particles, as detailed in this PCGS article. Apparently, the PVC flips attract microscopic particles which become embedded in the irregular surfaces of the flips. As a coin is slid in and out of the flip, these rough surfaces scratch the coin. While Mylar flips mitigate this problem, it is not completely eliminated. Therefore, care should be used when inserting and removing a coin from a flip, especially a PVC one.

 

Any flips I receive from dealers I treat as suspect, and usually throw them away. I never keep flips which I do not know the source of. While most dealers are conscious of the difference and the harms, you can never be sure. Also, you never really know how old the flip is - it might be from some old collection before these dangers became apparent. The TPGs used to use PVC flips for returning body bags, but I learned recently from NGC that they no longer use PVC flips. Be aware that some auction houses will still ship and store coins in PVC flips. For example, Heritage is notorious for this!

 

Mylar flips are safe for coins. It is very difficult to distinguish a Mylar flip from a PVC flip just by looking at them. Try bending and folding a flip - if it is Mylar it will feel more brittle. A PVC flip will feel more pliable. Also, try smelling the flip. Just like residue on a coin will smell like shower curtains, a PVC flip will sometimes smell like shower curtains. This is not foolproof, so do not use this as a certain test; as the plastic ages, the smell gradually fades away. The best way to be sure you are using Mylar or some other safe plastic is to note the packaging it came out of - it should say.

 

The other way to tell is to do a flame test – but be careful with this! Wear fireproof gloves so you don’t get burnt, safety goggles so you don’t go blind, do it outside in a well ventilated area so you don’t inhale toxic fumes, etc. Take a wire, and sterilize it by holding it in a flame until the fame burns clear. Melt a piece of the plastic on the wire, and then hold this in the flame again. If the flame burns green, then you have PVC. For more on flame tests, see this link.

 

Some people argue that PVC flips are okay for short term use. I disagree, but if you choose to use PVC flips, I would recommend not keeping them there for more than a month. The rate of Hydrochloric acid release is dependent on several factors, most important of which are temperature and humidity. Some coins have been stored in PVC for years and not been harmed, but others have been in PVC for a week and developed a film. This is especially noticeable on Proof coinage. Be careful when using PVC. I say if there is any chance of harming your coins, why use it at all?

 

Join me next weekend for a scientific discussion of acetone, and why it works so well on PVC!

 

[ldhair]

Great information. Glad to see you bringing up the auction house holders. Many don't think twice about them. I learned the hard way years ago. It was a costly lesson. Looking forward to the next two parts.

[murty]

Very informative...looking forward to next installments.

[michael]

thanks for posting this great information!

 

i look forward to parts 2 and 3

[coinman_23885]

This is an excellent post (as always). I think this post belongs in the "What You Need to Know - About Coin Collecting" forum, as it will be quite useful for years to come. I look forward to installment two and your discussion of organic chemistry (it will bring back memories for me from my organic chemistry classes a couple of years ago).

[WoodenJefferson]

This is one of those (thumbs u occasions. Nice stuff there Jason.

[delta]

Many thanks for posting these essential details.