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Evaluating Safe Preservation Methods for Proof Coins

Proof Coins

By Joshua McMorrow-Hernandez for CoinWeek.com ……
For as long as there have been Proof coins, there have been collectors trying to preserve them. Proof coins, which are often struck more than once (at least twice) on polished planchets by specially prepared dies, are specifically designed to be appreciated and are not intended for use in general circulation.

During the 19th and early 20th centuries (the early years of Proof coin production in the United States), it was presumably much more difficult to spare these collector coins from the damage that can ruin their beautiful, crisp surfaces. Proof coins are veritable magnets for fingerprints, spots, haze and other undesirable surface issues.

Damaged Proof coins are typically known as impaired Proofs, and they are usually worth only a mere fraction of the Gem or Brilliant Proof coins representative of the epitome of Proof coin quality. Of course, not all Proof coins boast brilliant surfaces – a point well exemplified by the Matte Proof coins commonly struck during the 19th and early 20th centuries. Even without fragile, mirror-like devices and fields, these Matte Proofs are easily susceptible to visible damage and are no less sensitive to mishandling than their Brilliant Proof counterparts.

While early Proof coins weren’t originally preserved in cellophane envelopes or rigid plastic cases (as has been the case since the modern Proof coin era began in the United States in 1936), there are still plenty of stunning Proof survivors from that earlier period. Conversely, there are countless impaired modern Proofs that have been damaged due to mishandling, improper storage, or other forms of neglect.

One can thank the meticulous numismatic stewards of previous generations for the gorgeous early Proof coins that exist today.

Educating Collectors on Proper Storage

Keeping Proof coins well preserved seems to elude some collectors, in part due to circumstantial storage situations but in other cases due to a simple lack of knowledge on the subject. The United States Mint has worked to educate its proof coin customers on how best to preserve their purchases. For example, in the early 1960s, the U.S. Mint packaged its Proof sets with a paper insert bearing the following care instructions:

This package was designed to prevent or delay tarnishing and discoloration. Nevertheless sooner or later tarnishing may occur. Care in handling and storing will help to prolong the newly minted luster of the coins. Heat and direct sunlight are especially harmful.

By the early 1990s, the United States Mint included the following, more specific storage recommendations:

To preserve the beauty of your Proof coin set store in a cool, dry place.

Condensing this pair of instructions down into a single set of guidelines, one would surmise that the optimal condition for Proof set storage is a cool, dry location away from direct sunlight. Yet the proper storage of Proof coins, not to mention collectible coins in general, is much more complex than these seemingly simple instructions may suggest. Pollutants, temperature variance and physical handling of the coins are all volatile variables that can affect how well your Proof coins fare over the long term.

Having said that, yes, a cool, dry place away from direct sunlight is an ideal location for storing your Proof coins. This can mean storing them in a vault, a safe, a cabinet, or some other similar structure tucked away from exposure to heat and intense light. The additional consideration of keeping coins in a dry location also implies they should be kept in a climate-controlled environment. Thus, storage in an attic, basement, garage, commercial storage unit–or even a recreational vehicle such as a camper–could increase the risk of environmental damage to Proof coins.

But there’s still much more to the proper storage of Proof coins than even these recommendations require. Unsurprisingly, thorough addressing of the issue would probably necessitate that the Mint issue an entire booklet of care instructions. Of course, that isn’t likely to be feasible due to package space constraints and production costs. Even if care booklets were included with Proof sets, one wonders how many people would actually read them from cover to cover.

1942 Proof QuarterIndeed, a lack of education in the field of Proof coinage preservation may be one reason why countless millions of formerly brilliant, gorgeous Proofs have become spotted, hazy, or otherwise lackluster in appearance. But collector negligence isn’t the only reason why so many exhibit signs of damage.

There are myriad uncontrollable factors, too, including humidity and air pollutants. For example, coin collectors in Florida experience oppressive air humidity on an annual basis from the months of May through October. Hobbyists living in Martha’s Vineyard, Massachusetts, are surrounded by the Atlantic Ocean on all sides and therefore must contend with the salty sea air. In Los Angeles, California, consistently high levels of air pollution can wreak havoc on coins.

There are also hidden problems on some Proof coins that misfortunate collectors don’t cause themselves but merely inherit. For example, milk spots are notorious on Proof American Silver Eagles, and these blotchy white patches are attributed to a detergent residue leftover from planchet preparation. These white spots can appear months or years after the coin was minted, regardless of whether the coin is stored in its original government holder, a third-party certified slab, or a vacuum-sealed vault in the aridest of deserts.

Another issue plaguing coin collectors is festering damage from exposure to polyvinylchloride, or PVC. Many early and modern individual Proof coins have been stored in aftermarket flips, albums and holders laced with the destructive plastic agent. Often, PVC damage shows up long after the coin’s exposure to the chemical; a collector may unknowingly buy a coin that was once exposed to PVC only to find the coin acquiring the telltale, irreversible signs of its wrath, including sea foam green patches or cloudy haze across the surface years later.

Expert Tips on How to Preserve Proof Coins

“The Mint’s recommendations [as listed on the Proof set inserts] are great,” says Richard Montgomery, president of Numismatic Guaranty Company (NGC). Indeed, a cool, dry location away from direct exposure to sunlight is a key factor in preserving Proof coins.

But Montgomery says there are several other keys to keeping Proof coins in the best condition, including environmental consistency.

“Constancy in temperature is important. You really don’t want big swings in temperature, because that can have an effect on the metal.”

What about the holders? What should Proof coins be stored in?

“Original Mint holders are very good, especially the modern ones,” Montgomery comments.

And as for the older cellophane flatpacks of the 1950s and ’60s? “They keep the coins decently safe and are probably fairly inert.”

He says advanced 21st-century holders could help better preserve those older Proof coins.

“But that’s the contrarian problem,” he adds. “The collector believes if they see a Proof coin in its original holder that it’s worth more, but that holder may not be the best environment for the coin.”

1964 Proof Half DollarOne could therefore draw the conclusion that the Proof sets left in their original holders are certainly adequate, especially if they are undamaged, and that the coins will likely be just fine if they are not removed. However, for Proof coins that have been removed from their original holders or those that are already sold as singles, Montgomery says inert Mylar flips are good for safe, inexpensive storage.

Holders are an important consideration in the safe storage of Proof coins, but so is the environment around the holder. Exposure to air pollutants is a well-known cause of myriad surface issues. But what may not be as well understood is what exactly qualifies as a pollutant, a category that includes several elements common to many households.

One of the most nefarious? Tobacco products.

“Smoke can seep into coin holders, especially loose flips,” explains Montgomery. “[Tobacco smoke] can also be a problem if coins stored in holders or albums are removed for viewing in the home.”

Other common household pollutants include cleaners, car exhaust in or near garages, and naturally occurring ground chemicals like sulfur that may be found in or around basements.

“It’s really important that Proof coins, or really any coins, be kept in a clean environment,” he stresses. “As long as the air is clean, the coins should fare well.”

The use of dehumidifiers and air purifiers in the home can help toward this end. Montgomery also says collectors should do their best to keep their coins in a stable setting.

“Maybe they should just keep their coins with their wine in the cellar,” he chuckles.

Just don’t keep the coins in the wine.


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  1. I have done everything right with my proofs . temperature control , no smoke , no sunlight , dry , in original containers . air purifier etc. and still getting a haze on my coins. How can you call them presentation coins when they cant be maintained for being what they call them ? I’m also constantly replacing state quarter silver mint sets because they keep fogging up in perfect condition for storage and found out a long time ago they had problems with the cases back in the day do the most problematic are 1999-2003 years !! the priciest ones !!


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