To coin collectors, PVC may as well be a four-letter word.
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Images courtesy of Numismatic Conservation Services. Copper and copper-nickel coins are more susceptible to PVC damage than coins of other metals, particularly to an affliction known as green slime. The reverse of this 1923-S Indian Head 5-cent coin bears the green slime caused by PVC. The "after" image at right reveals what it looks like after being conserved through NCS.
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Images courtesy of Numismatic Conservation Services. An Anthony dollar exhibits a milky, hazy residue in the fields, a residue caused by PVC contamination. The coin looks much different at right after conservation from professional service, in this case Numismatic Conservation Services.
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Coin World photo. Commercial products like Koinsolv provide one way for collectors to remove PVC contamination from affected coins.
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Images courtesy of The Coin Collector's Survival Manual. A Walking Liberty half dollar bearing black spots caused by PVC contamination was professionally conserved and the spots were removed.
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Courtesy of The Coin Collector's Survival Manual. This 1963 Lincoln cent, once graded Proof 70 by Professional Coin Grading Service, exhibits PVC damage, according to author Scott Travers. Arrows highlight the areas with the most damage. PCGS had to buy the $39,100 coin back when damage appeared after certification.
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PVC, or polyvinyl chloride, has wreaked havoc to immeasurable amounts of coins through the years, leaving its sticky, slimy mark on many a "Mercury" dime and a bevy of "Buffalo nickels," just to name a few.
The bad news is that PVC is a surface contaminant, an unwelcome gift from the wrong kind of coin holder. But, the good news is that PVC can be detected and removed.
Of course, the easiest way to ensure your coins do not get contaminated by PVC is to avoid the pliable, soft plastic "flips" that are often used to store coins.
What is PVC?
A chemical added to the flips when they're being made, a plasticizer to make them soft, is the culprit.
Not all plastics contain PVC. According to Susan L. Maltby, author of the monthly "Preserving Collectibles" column in Coin World, "Recommended materials include polyethylene, polypropylene, polystyrene, Mylar D (polyethylene terephthalate), Kodar (similar to Mylar D) and polymethyl methacrylate (e.g., Plexiglas)."
She strongly recommends against using holders made with PVC.
PVC can deposit chemical plasticizers on a coin, releasing hydrogen chloride gas. At high temperatures that can easily be achieved in a home during the summer, for example, the gas reacts with humidity in the air and forms hydrochloric acid, which can eat into the surface of a coin, according to Scott Travers in The Coin Collector's Survival Manual, sixth edition.
PVC manifests itself as sticky greenish and blue flecks and stains, according to George Klabin in Understanding PVC Damage, cited in Travers' book.
"When viewed with magnification, these flecks appeared to be thick, sticky, colored liquid which rested on the coin surface, or else appeared as patches of colored stains," Klabin wrote.
When coins affected by PVC are removed from the offending plastic holder, a green or blue ring remains on the holder where the coin rim interacted with it. In severe cases, the coins are themselves stuck to the plastic holder and have to be removed with force, and severe damage, Klabin notes.
Coin dealers often still use PVC holders despite this, Travers wrote.
"Dealers don't have to worry about the negative effects because they move their inventory so quickly," Travers writes. "In fact, I recommend the PVC flip-type holders if you're taking a lot of coins to a coin show for a couple of hours. These pliable pouches allow ease of handling, as well as an unobstructed view of the rim and edge. Just don't leave the coins in these holders for more than an hour or two, and don't expose the holders to heat."
Certain roll holders also contain PVC and should be avoided. Travers said only the "squared-off milky polyethylene" tubes are inert.
PVC affects coins of different compositions differently.
Gold and platinum coins are least affected, or most resistant, to damage, with silver coins next. Copper and copper-nickel coins are the most susceptible to PVC damage.
Colors can range from nearly white to dark green or gray, according to the Web site for the grading service ANACS. Copper coins will gain a greenish slime or spots from PVC, and silver coins gain what is often described as a milky haze.
Also look for light milky spots on the coin, as PVC residue can appear as streaks or a light haze.
Get a whiff of this
Maltby wrote in the Aug. 25, 2004, issue of Coin World that collectors should avoid plastic holders that have a chemical odor, as that is often an indicator that the holders are "loaded with plasticizers and other fillers" that will adversely affect your collection.
You can use your sense of smell to detect whether a coin has PVC contamination. It will smell like a new plastic shower curtain, according to the Web site for ANACS.
If you sense PVC contamination has occurred, remove the coin from the holder if it is still housed in one.
Maltby suggests using the Beilstein test to confirm whether a holder is indeed laden with the offending substance. Maltby provided the steps for the test in her Aug. 25, 2003, column.
To carry out the test you will need a small propane torch and a copper wire. Copper by itself burns cleanly but produces a green flame (copper chloride) when combined with a compound containing chlorine, like polyvinyl chloride.
A small scrap of heavy gauge electrical wire, with its plastic coating stripped, works quite well. Placing the wire in a wine cork makes it easy and safe to hold the wire in the flame.
Heat the copper wire until it burns cleanly. This is particularly important if you are using a new wire, to burn off any unwanted residues that might be on the wire. It also ensures that no plastic is left over from testing another holder.
Touch the hot wire to the holder. Some of the holder will melt and stick to the wire. Be sure to hold the holder close to the air intake of the torch in order to draw away the fumes from the burning plastic.
Put the wire back into the flame. If the flame burns yellow or clear, no PVC is present. If the flame burns bright green, PVC is present.
A positive finding is not a positive thing, as that means you'll have to replace all of the other holders of the same type you may be using and remove any possible PVC contamination from the coin the holder housed.
Removing PVC contamination
In a 2004 column, Maltby said that collectors should degrease coins to remove any plasticizer that may be on the surface before rehousing them.
Maltby said odorless mineral spirits "works quite well."
Apply and remove the solvent with a cotton swab, changing the swab regularly. Maltby suggests using a swab over dipping the coin into a solution of mineral spirits because it gives you more control and you are less likely to contaminate the solvent with the corrosion product (which will happen if you dip enough coins in the solvent).
Let the coin dry before placing it into a new, and safer, holder.
Some dealers and collectors advocate the use of acetone as a degreaser, but Maltby does not find it very effective, she wrote.
At Coins.About.com, author Susan Headley suggests using an acetone bath to remove PVC. Do so in a well-ventilated area away from any open flame, while wearing latex gloves and eye protection.
Most coins are stubborn to give up their PVC contamination, and Headley suggests using a cotton swab on these coins. After soaking the swab end in acetone, roll the swab across the affected area, being cautious to avoid rubbing the coin (too vigorous use of the swab could cause hairlines). Use more than one swab if needed, as the swabs get dirty. Particularly stubborn coins may require soaking in the acetone bath for 24 hours before using the "rolling" method again.
As a last resort, collectors may consider sending the coins to a professional conservation service, Headley suggests, listing Numismatic Conservation Services (which Travers also recommends).
According to Scott Schechter, vice president, sales and marketing for the Certified Collectibles Group (which includes NCS), NCS always advises that collectors seek the services of professional conservators, even where seemingly accessible techniques are often used.
NCS offers services to clean "dirt and agents that hide or might be harmful to an object's natural and original state. Proper cleaning takes into account original materials and finishes. It studiously avoids damaging original materials and finishes."
A full list of the firm's services is at its Web site, www.ncscoin.com.
Another option is a hobby product called Koinsolv, a neutral solvent that its marketer claims can clean numerous contaminants from a coin's surface harmlessly.
Though PVC may be a foul substance, and a foul word in numismatics, it doesn't have to be the final word. With either basic or advanced techniques, collectors can save their coins from the silent plague of PVC.
