How to store coins without losing value
Updated:
A coin that has survived for centuries can be ruined in a few months by bad packaging, damp or over-enthusiastic cleaning. Below are the most important storage rules, which protect condition and therefore the value of your collection.
Do not clean coins
This is the most important rule. Cleaning, especially mechanical and chemical, removes the natural patina, leaves hairline scratches and dulls the surface. Such a coin loses more value than one that is simply dirty or dark. Collectors and graders recognise the signs of cleaning, and grading companies label such coins as cleaned (“details”) and grade them lower.
If a coin comes from a dig and is covered with soil, do not try to restore it yourself. Consult a specialist, for example a conservator. In NumiStack you can mark on a coin that it has been cleaned so that this information is not lost.
How to handle a coin
- Hold it by the rim, between thumb and forefinger, and do not touch the surface of the obverse or reverse.
- Examine it over a soft surface (a towel or cloth) so that a fall does not damage the coin.
- Wash and dry your hands thoroughly. Fingerprints leave marks that eat into the surface over the years. If you use gloves, choose nitrile ones; cotton can snag on the relief.
- Do not talk or breathe over a coin, because droplets of saliva also leave marks.
Choose the right holders
Not every holder is safe. Choose chemically inert materials and avoid those that release harmful substances over time.
| Holder | Verdict |
|---|---|
| Cardboard holders with a PET (Mylar) window, acrylic capsules | safe; a popular choice for long-term storage |
| Albums with PET pockets and acid-free paper | safe if marked “PVC-free” and “acid-free” |
| Grading-company slabs | safe; they protect the coin and serve as a record of the grade |
| Soft flips and pockets made of PVC | avoid; plasticisers released by PVC can leave a greenish film on coins |
| Ordinary paper, cardboard and rubber bands | avoid; they can contain sulphur and acids that speed up the tarnishing of silver |
Humidity and temperature
Moisture is the main enemy of coins. It promotes corrosion of copper and bronze (green deposits), spots on silver and damage to holders. A moderate, stable humidity, usually in the range of 30–50%, and a steady temperature without sudden swings are recommended.
- Do not keep coins in a bathroom, a cellar, an attic or near a radiator.
- Put a moisture absorber, such as silica gel, in the cabinet or safe and replace or regenerate it regularly.
- Ventilate the room. Do not shut coins in airtight containers with damp air inside.
- Silver tarnishes from sulphur compounds, so avoid rubber, wool, some paints and rubber seals near coins.
Protect the collection from theft and fire
Keep valuable coins in a safe (ideally anchored to the floor or wall) or in a bank safe-deposit box. Do not advertise your collection: the fewer people who know about it, the better. Consider insuring it. An insurer will usually require a list of coins with photos and values.
Remember that the documentation of a collection should not be kept in the same place as the coins. Keep a copy of the inventory with photos and valuations off-site, for example in the cloud or on a drive in another location. How to build such an inventory is described in How to catalogue a coin collection.
Label where everything is
Each coin should have its storage place recorded and its holder clearly labelled with the inventory number. Label the cardboard holder or the pocket, never the coin itself. In NumiStack you record the place hierarchically: warehouse, room, safe, drawer, album, page and position, so a year later you know at once where to look. Before a coin goes into the safe, record its grade according to the grading scales and any defects you can see.