Understanding Professional Numismatic Conservation

Posted by Brian A. Silliman on 2/7/2003

The improper cleaning, handling and storage of coins are major problems in this hobby. Anyone who has collected coins, even if only for a short time, has seen otherwise great coins that have been damaged...

This article originally appeared in Volume 51, Number 31 of Numismatic News, a Krause publication.

The improper cleaning, handling and storage of coins are major problems in this hobby. Anyone who has collected coins, even if only for a short time, has seen otherwise great coins that have been damaged or had their eye appeal negatively affected by hairlines, impaired luster, unnatural color, severe tarnish, residues or other contaminants.

Until recently, collectors and dealers did not have many options in rescuing coins that display harmful surface conditions. Professional conservators routinely conserve ancient coins, especially those recovered from archeological sites. Most other coins especially coins of more recent vintage, have been largely overlooked and not conserved professionally. A notable exception of recent memory is the SS Central America coins that were conserved after being salvaged from the sea and brought back to terra firma.

Other than these examples of professional conservation, the vast majority of coins in the market place that could benefit from conservation have been left to the amateur cleaning effort of collectors and dealers or have not been conserved at all.

While a coin can be properly cleaned, where by contaminants, debris, corrosion, tarnish and a variety of harmful residues are removed without altering or impairing the coin's original surfaces, many have been damaged by improper "cleaning". The unfortunate irony of the situation is that in the process of trying to save a coin or improve its appearance, many coins suffer even more severe and irreversible damage such as hairlines, impaired luster, color changes or develop corrosion from inadequate neutralization.

To understand the basis and need for professional numismatic conservation we need to understand how and why coins deteriorate and the conservator's role in remedying or reducing detrimental surface problems.

Coins are prone to corrosion as a result of their composition. The metallic composition and durability of coins is one of its major advantages, but it is also a hazard. Coins are actually very fragile and can be damaged or even destroyed very easily.

Coins are most often produced in copper, nickel, silver or gold. All of these metals are produced from ores that are smelted from a mineral state that is relatively stable to a crystalline solid or metal state that is somewhat unstable. Virtually all coinage metals are a mixture of more than one metal. A mixture of metals is used to produce a particular coinage alloy in order to attain certain desired characteristics such color, intrinsic value and durability.

Luckily for us, coinage metals are fairly durable, especially in comparison to other materials that have been used for money over the centuries. Had the Greeks or Romans used paper money instead of coinage, surviving specimens would be so rare and fragile only a collector that is as rich as Croesus could afford them.

A coin's survival and state of preservation are influenced by the coin's environment and this is due to interaction with the coin's metallic composition. Take for example the survival of ancient Roman coins found at archeological sites. Coins found buried in earth consisting largely of limestone or alkaline soils, as may be found in farmland or countryside, may be in relatively good condition and have only minor spots of corrosion and encrustation. In situations like these, some coins may develop a patina, which actually protects the coin from severe deterioration. On the other hand, coins from granite sub soils common to more urban environs and areas of bedrock can be found heavily encrusted, deformed and corroded by the acids in the gravel and sands. In the most severe cases, these coins corrode and deteriorate almost completely.

While coins produced during the last couple of centuries are less likely to be found with extreme problems like this, they commonly have debris particles, residues and other potentially corrosive elements on their surfaces.

Debris particles are often found stuck in the recesses of design elements. These particles can contain corrosive causing elements which overtime can develop into severe spots of active corrosion

Other harmful surface conditions result from the handling and storage of coin collections. Even the most careful of handling enables contaminants on your fingers to be transferred to your coins. Oils and salts are continuously secreted through the skin and will be transferred to the coin along with many other potentially harmful elements that adhered to the skin through contact with other items. To avoid putting very noticeable and often irremovable fingerprints on the fields of a coin, emphasis is placed on handling coins by their edge, but even this allows residues to transfer. You can sometimes see this on early copper coins where the obverse and reverse may display an attractive brown color while the rim has a slightly lighter and pink coloration from contact with fingertips. In more extreme examples, the obverse and reverse may appear to be in very good condition while small green spots of corrosion are visible on the edge and rim.

In an effort to avoid handling coins, a wide variety of storage devices have appeared on the market place. Over the years, hundreds if not thousands of different products ranging from flips and envelopes to books and boxes have been sold to help collectors store and manage their collections. The earliest versions were not with out problems. Many holders contained sulfur, PVC and a variety of other possible contaminants. In recent decades, manufactures have become more informed and responsible and we have seen the development of much safer storage products. Nevertheless, not all collectors and dealers seek out these coin friendly products, while many hobbyists have not removed their coins from the old and potentially hazardous holders. Coins from improper holders are seen often in the market place. PVC contamination is one of the more commonly seen problems resulting from bad coin holders and in many cases corroded into the surfaces of the coin.

Even if coin friendly holders are used, the surrounding environment can still adversely affect a coin's condition by facilitating corrosion or tarnish.

Lets be honest with ourselves about "toning". When a coin has an attractive pattern of colors it's called "toning". When it's unattractive it's called tarnish or spots. And when it is very dark it's often called environmental damage.

The terrible truth about tarnish is that it is a form of oxidation and is primarily caused hydrogen sulfide and carbonyl sulfide. Tarnish can result from direct contact with tarnish-causing elements or through vapors.

Some common tarnish-causing elements are wool, silk, felt, dyed fabrics, paper, cardboard, wood and wood products to name just a few. In short, traces of tarnish-causing elements can be found all around your house, office or shop and even in the clothes you are wearing. Keep in mind that while you may not be able to smell sulfur (a rotten egg smell) until it reaches unhealthy levels, coins are more than one hundred times more sensitive to it. Add fluctuations in temperature and humidity to the mix and the speed and effect of the tarnish-causing materials is increased.

Coins displaying the effects of any of the aforementioned hazards are prevalent in the marketplace. Their appearance may vary considerably, but it is generally unappealing and will usually get worse over time. Likewise, the results of amateur attempts to address these problems are also easy to find in the many improperly cleaned or "problem" coins that display hairlines, scratches, impaired luster, uneven or unnatural color.

The difficulty dealers and collectors experience in attempting to conserve their coins is that they lack the technical expertise, appropriate materials and, more importantly, experience and training. Conservation is much more than just "dipping" a coin and drying it off. A treatment like this may impair or damage as many coins as it helps. It also leaves the coin susceptible to advanced corrosion, as dip residues become corrosive over time.

Professional numismatic conservation has grown out of the need to save coins from detrimental surface problems and preserve our numismatic heritage, while also providing hobbyists with a safe alternative to cleaning coins on their own.

While professional conservation may be relatively new to this hobby, other cultural and historical artifacts have been routinely conserved for a very long time. Conservation is a very specialized field and conservators usually focus on one type of artifact or conservation method. This specialization is necessary because they must possess tremendous knowledge of the item they are conserving. They must be experts in evaluating the composition, production and condition of the item in order to be able to master the complexities of treating the item to produce successful and consistent results. This specialization along with extensive hands on experience ensures the conservator will make sound judgments during the evaluation and subsequent conservation.

Before any procedure is undertaken, a careful and thorough evaluation of the coin is made. During this detailed analysis, the evaluator assesses the condition of the item's underlying surfaces, identifies the surface problem(s) and makes a determination as to what, if any, treatment will be most beneficial in removing or reducing the contamination and stabilizing the coin to limit further deterioration. The coin's manufacture, age, composition and grade are especially important because they influence which procedure will be most effective in producing results of the highest standards.

Since the evaluation process is every bit as important as the procedure undertaken, the evaluator has to have seen hundreds of thousands of coins, understand their production and the subtleties of their luster patterns, color and originality.

Unlike other conservation specialties, the certified grading system makes the job of the evaluator very difficult. When reviewing certified coins the evaluator must determine if the coin will maintain its current grade after conservation. Even though, the procedure only removes foreign material from the coin, these materials may conceal minor marks that may affect grade once the coin's true surfaces are visible again. This is a very important consideration, especially when only very slight differences in luster brilliance can mean the difference between a coin grading MS68 or MS67.

Having the most experienced evaluators and foremost conservation experts working in unison ensures results of the highest caliber, while reducing the risk of a coin not maintaining its current grade. In many cases, when all of the elements work well together, coins can and do increase in grade, as their original surfaces become visible and unimpeded by residues

After the specimen has been evaluated and a procedure is prescribed, the coin is conserved in a laboratory setting specifically designed and equipped to ensure consistency and quality of the results. Through the systematic application of chemicals and solvents, the conservator is able to reduce or remove the detrimental surface conditions while protecting the original integrity of the coin's surfaces. In some cases, several different treatments may be used to address several different contaminants. In addition to removing foreign materials the procedure also neutralizes the coin to ensure longer-term stability.

The most important difference between numismatic conservation and many other conservation specialties is in regard to the restoration of the object. In other fields it is acceptable to "strip" down the item and its outermost original surfaces and then restore the item by rebuilding its surfaces before applying preservative materials. For obvious reasons, this is not acceptable in numismatic conservation where the principle goal is to remove detrimental foreign materials and protect the originality of the specimen's surface.

Much like the early years of certified grading, numismatic conservation has seen its fair share of controversy. However, as collectors and dealers gain a better understanding of the principles of professional conservation and how beneficial it is in the preservation of our numismatic heritage, the hobby will hopefully see a reduction in the number of "problem" and improperly cleaned coins in the market place.

At present, there is very little useful information available on numismatic conservation, especially as it pertains to more modern coins. However, the booklet, The Conservation of Coins; A Buyers Guide is helpful in gaining an understanding of importance and uses of professional conservation and the problems associated with improper cleaning. This booklet is a collaborative effort on the part of PNG, NGC, PCGS, ICTA and ICG. It can be viewed by clicking here

This article was originally published in Numismatic News on July 30, 2002. Numismatic News is published by Krause Publications, Iola, WS.

Return to the Articles List









  • Global Locations
  • Germany
  • Switzerland
  • Singapore
  • China
  • Hong Kong
  • Taiwan
  • South Korea
  • Global locations map
  • Contact Us
  • NCS
    P.O. Box 4750
    Sarasota, FL 34230
  • 1-866-NCS-COIN toll free
    +1 941-360-3996
    +1 941-360-2559 fax
    Service@NCScoin.com
  • Hong Kong
    NGC-NCS-PMG
    Tsim Sha Tsui, Kowloon
    Hong Kong
    +852 2115-3639
    Asia@NCScoin.com
  • Switzerland
    NGC-NCS-PMG
    Zurich, CHE
    +41 43 816 28 16
    Europe@NCScoin.com
  • Germany
    NGC-NCS-PMG
    Munich, Germany
    +49 89 255 47 545
    Europe@NCScoin.com
  • Numismatic Guaranty Corporation
  • Paper Money Guaranty
  • Comics Guaranty, LLC
  • CGC Magazines
  • Collectors' Society
  • Certified Collectibles Group
  • Official Conservation Service of

    ANAPNG

    © 2014 Numismatic Conservation Services, LLC | Legal Notice and Usage Restrictions | 866-NCS-COIN