Coin Storage and Preservation
A complete guide to the principles, materials, and methods of long-term coin preservation — written for collectors of the Australian decimal series.
A collection is only as good as the conditions in which it has been kept. The coins most collectors prize are those whose condition has been preserved — and condition, for uncirculated and proof specimens, is almost entirely a function of storage.
Why Coin Storage Matters
A coin's condition determines its numismatic value. For circulating coins this is determined by wear, but for uncirculated, proof, and high-grade specimens — the coins most collectors prize — condition is determined almost entirely by how the coin has been stored and handled since it left the mint. Improper storage is the leading cause of condition deterioration in otherwise preserved coins.
The three primary threats to coin preservation are physical contact damage, chemical reaction from reactive storage materials, and environmental exposure to humidity, temperature variation, and airborne pollutants. All three can be substantially mitigated through correct storage selection.
For the Australian decimal series specifically — a series produced predominantly in cupro-nickel and aluminium bronze — the reactivity of storage materials is the most commonly overlooked risk. Many collectors unknowingly store significant collections in materials that are actively degrading coin surfaces over time.
The Primary Threats to Coin Preservation
Physical contact and handling damage
The oils, acids, and salts on human skin cause permanent fingerprint marks within hours of contact. Micro-abrasions from coins moving inside ill-fitting recesses reduce grade irreversibly. Even a single mishandling of a proof coin can cause detectable surface damage.
Reactive storage materials
PVC-based foam and plastic holders off-gas chlorine compounds that react with copper alloys — the primary metal in all Australian decimal coins. The result is PVC haze: a greenish, sticky film that cannot be safely reversed. Prevention is the only solution.
Humidity and temperature variation
High relative humidity accelerates oxidation and toning on copper-alloy coins. Temperature swings cause expansion and contraction in both coins and storage materials. Stable conditions between 40–55% relative humidity and 18–22°C are ideal.
Airborne pollutants and light
Hydrogen sulphide from rubber, adhesives, and environmental sources causes toning over time. Direct sunlight causes colour change on proof coins and toned specimens. Sealed cases in low-light environments provide effective protection against both.
The Problem with PVC in Coin Storage
Polyvinyl chloride — PVC — is used extensively in inexpensive coin storage products including soft plastic coin holders, album pages, and the foam linings of many mass-produced display cases. PVC is problematic for coin storage because it is chemically unstable over time. As PVC ages, it releases plasticisers and, critically, chlorine-containing compounds that react with the metals in coins.
The visible result of PVC damage is a greenish, sticky film on the surface of affected coins. This film is a product of the chemical reaction between chlorine compounds from degrading PVC and the copper content of the coin. Australian decimal coins in the 5 cent, 10 cent, 20 cent, and 50 cent denominations are all cupro-nickel — 75% copper — making them particularly susceptible. The $1 and $2 coins are 92% copper aluminium bronze, also highly reactive.
PVC damage is not reversible without risk to the coin's surface. Professional conservation can remove PVC haze using acetone in controlled conditions, but any treatment carries a risk of altering the coin's surfaces and affecting its grade. The only reliable solution is prevention.
Soft, flexible plastic holders that feel slightly oily are almost certainly PVC-based and should not be used with valued coins.
Rigid plastic holders marked “Mylar,” “polyester,” or “polypropylene” are generally safe for coin storage.
Foam linings in display cases should be confirmed as archival-grade and PVC-free before use with any coin you intend to preserve. If the foam is not explicitly described as archival or inert, assume it is not.
Archival Materials in Coin Storage
Archival-grade materials are materials that have been tested and confirmed to be chemically inert — they will not off-gas, react with, or leach compounds onto the objects they contain. In coin storage, archival materials are those that will not interact with coin surfaces under normal conditions over extended periods.
Archival foam
The standard lining material for quality coin display cases. Genuine archival foam is closed-cell, chemically inert, and free from PVC, sulphur compounds, and acids. It is firm enough to hold coins securely in precision-cut recesses without compressing or deforming. Thomas Anne cases use archival-grade inert foam in all coin recesses.
Coin capsules
Acrylic or polystyrene capsules provide individual coin protection within a display case. The capsule completely encloses each coin, preventing contact between the coin surface and any foam or case material, and protecting against airborne moisture and pollutants. Thomas Anne cases are supplied with the appropriate capsules for each denomination.
Mahogany Family Hardwood
The timber used in Thomas Anne cases is chemically stable and produces no off-gassing compounds harmful to coin surfaces. Composite timbers such as MDF and particleboard may emit formaldehyde from the resins used in their manufacture. Solid hardwood does not carry this risk.
Solid brass hardware
Specified for all Thomas Anne locks and hinges because brass is corrosion-resistant under normal storage conditions. Plated metals corrode when the plating degrades, and corrosion products can transfer to coin surfaces if contact occurs. Solid brass avoids this risk entirely.
Physical Handling: Preventing Contact Damage
The oils, acids, and salts present on human skin cause permanent fingerprint marks on coin surfaces within hours of contact. On proof coins — which have mirror-like surfaces and frosted relief — a single fingerprint can reduce a coin's grade by one or more points, translating to a significant reduction in value. On uncirculated specimens, fingerprints are equally damaging though sometimes less immediately visible.
The standard practice for handling valued coins is to wear clean cotton inspection gloves, hold the coin by its edge, and never touch the obverse or reverse surfaces. Thomas Anne includes cotton inspection gloves with every case for this reason.
Coins should never be slid or dragged across surfaces. Even microscopic particles of dust between a coin and a surface act as abrasives, causing hairline scratches visible under magnification. Coins should be lifted cleanly and placed cleanly — never dragged.
When examining coins through a loupe or microscope, ensure the examination surface is clean and padded. Dropping or striking a coin against any hard surface can cause contact marks that permanently affect grade.
Environmental Conditions for Coin Storage
Humidity is the most significant environmental threat to coin storage. High relative humidity accelerates oxidation and toning on copper-alloy coins. The recommended relative humidity range for coin storage is 40 to 55 percent. In humid Australian climates — including coastal South Australia — this may require climate control or silica gel desiccants in storage areas.
Temperature variation causes expansion and contraction in both coins and storage materials. Stable temperature is more important than a specific temperature level — a consistent 18 to 22 degrees Celsius is ideal. Avoid storing coins in rooms subject to significant temperature swings, such as garages, sunrooms, or rooms with large north-facing windows.
Light exposure can cause toning and colour change on proof coins and in toned specimens. Direct sunlight should be avoided entirely. UV-filtered display cases and storage in low-light environments are best practice for long-term preservation.
Airborne pollutants including hydrogen sulphide (from rubber, certain adhesives, and environmental sources) and chlorine compounds cause toning and surface damage over time. Storing coins in sealed cases significantly reduces exposure.
Coin Toning: Natural vs. Artificial
Toning is the gradual change in colour that occurs on coin surfaces as a result of oxidation and chemical reactions with the environment. On silver coins, toning can range from subtle golden hues through blues, purples, and greens to black. On copper and bronze coins, toning produces the characteristic reddish-brown to brown-black colouration associated with aged copper.
Natural toning — acquired slowly over decades through normal environmental exposure — is considered acceptable and in some cases desirable by collectors. Certain naturally toned coins, particularly silver specimens with attractive rainbow toning, command premiums at auction. Natural toning is considered part of the coin's history.
Artificial toning — induced through chemical treatment to simulate natural toning — is considered undesirable and is regarded as a form of alteration. Professional grading services can usually distinguish natural from artificial toning, and artificially toned coins are typically graded lower or noted on their certification. Collectors should be cautious of coins offered with unusually attractive or uniform toning, particularly from recent decades.
Why Cleaning Coins Harms More Than It Helps
Cleaning coins — even with materials marketed as safe for numismatic use — almost universally reduces their grade and value. The surface of an uncirculated or proof coin has microscopic flow lines from the minting process and a delicate lustre that is disturbed by any abrasive contact. Even the softest cloth, applied gently, leaves hairline scratches detectable under magnification.
The numismatic community's position on cleaning is consistent: do not clean coins. A coin with original surfaces — even if slightly toned or marked — retains more value than the same coin after cleaning. Professional grading services detect cleaning and designate cleaned coins accordingly, which significantly affects their market value.
If a coin has PVC damage or environmental contamination, professional conservation by a qualified numismatist is the only appropriate intervention. This should not be confused with cleaning — conservation aims to stabilise the coin without altering its surfaces, and is performed only when deterioration would otherwise continue.
A quality coin display case serves three functions simultaneously: it protects coins from physical contact and handling damage, isolates them from reactive materials and environmental pollutants, and presents the collection in a manner consistent with its significance. Not all commercially available cases meet all three criteria.
Thomas Anne Collectibles designs and manufactures display cases specifically for the Australian decimal collector. Each case uses precision-cut archival foam recesses sized to exact capsule dimensions, solid brass locks and hinges, and Mahogany Family Hardwood construction — materials selected for preservation performance rather than price point.
The Thomas Anne standard begins with the question: would we accept this case for our own collection? If the answer is anything less than yes, the case does not leave our hands.
Archival-grade display cases made to order in South Australia.
Mahogany Family Hardwood. Solid brass hardware. Inert foam recesses.
Thomas Anne Collectibles — thomasannecollectibles.com.au — South Australia, Australia. This guide is published as a reference resource for coin collectors. It does not constitute professional conservation advice. For significant or high-value collections, consultation with a qualified numismatist is recommended. Last updated April 2026.